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Raw and modified fibrous clay minerals palygorskite (Pal) and sepiolite (Sep) were tested for their ability to remove ammonium from ammonium polluted water. Palygorskite and sepiolite underwent thermal treatment at 400°C (T-Pal and T-Sep respectively). Raw and thermally treated samples were characterized using XRD, SEM, BET, FTIR, TGA, zeta potential, and XRF. The techniques verified the effect of thermal treatment on sample structures and the enhancement of negative charge. Both raw and thermally activated materials were applied in batch kinetic experiments, and found to be efficient adsorbents in their raw forms, since Pal and Sep achieved 60 and 80% NH4+–N removal respectively within 20 min of contact for initial NH4+–N concentration of 4 mg/L. Similar removal rates were gained for other concentrations representative of contaminated aquifers that were examined, ranging from 1 to 8 mg/L. Results for the modified T-Pal and T-Sep minerals showed up to 20% higher removal rate. Saturation tests indicated the positive effect of thermal treatment on the minerals since T-Pal and T-Sep removal efficiency reached 85% and remained stable for 24 h. However, competitive ions in real water samples can influence the NH4+–N removal efficiency of the examined samples. At almost all the examined samples, the nonlinear Freundlich isotherm and linear pseudo-second kinetic models showed better fitted all examined samples thus indicating heterogeneous chemisorption.

Palygorskite sample (Pal) underwent thermal treatment at 400 °C (T-Pal) to be used as adsorbent for the removal of 200 mg NH4+-N/L from artificial solution. After thermal treatment, the sample was characterized via X-ray diffraction (XRD) and scanning electron microscopy (SEM). For NH4+-N removal, T-Pal was added as a bed matrix in fixed-bed reactor experiments and the effect of flow rate was determined. It was indicated that with the flow rate increase from 10 mL/min to 50 mL/min, fewer liters of the solution were purified, rendering a longer residual time of interactions, which is optimal for NH4+-N removal from T-Pal. The maximum removed amount was calculated at 978 mg NH4+-N (qtotal), suggesting T-Pal is a promising ammonium adsorbent. The data of kinetic experiments were applied to Clark, Yoon–Nelson, and Thomas kinetic models, with Clark having the best fit, highlighting a heterogenous adsorption. At the end of kinetic experiments, T-Pal applied in hydroponic cultivations and presented a sufficient release rate, which was found utilizable for saturated T-Pal usage as N fertilizer that satisfactory results were deemed concerning lettuces characteristics and growth.

Palygorskite sample (Pal) underwent thermal treatment at 400 °C (T-Pal) to be used as adsorbent for the removal of 200 mg NH

In the present study, electrocoagulation (EC), alone or in combination with precipitation or centrifugation, was assessed as a potential pretreatment method for enhanced production of biofuels from 3-phase decanter olive mill wastewater (OMW). Experiments were performed using undiluted and diluted OMW in an EC reactor, operating with a current of 2 A and either Al or Fe electrode materials. Subsequently, diluted OMW was subjected to EC followed by precipitation or centrifugation. The effect of current density (0.05, 0.5 or 1 A) on the combined EC – centrifugation process was assessed and a high reduction of organics was observed for the higher current applied. The different fractions of the pretreated effluents were used as substrates for methane, hydrogen as well as for bioethanol production and the maximum energy recovery was determined in each case. It was shown that, EC at a current of 2 A or further combination with physical methods led to low biofuels yields. However, reduction of the current during EC to 0.05 A or 0.5 A, led to high methane and ethanol yields, with the best scenario being the production of methane yielding an energy equivalent of 1902 kJ/L OMW.

Raw and modified fibrous clay minerals palygorskite (Pal) and sepiolite (Sep) were tested for their ability to remove ammonium from ammonium polluted water. Palygorskite and sepiolite underwent thermal treatment at 400oC (T-Pal and T-Sep respectively). Raw and thermally treated samples were characterized using XRD, SEM, BET, FT-IR, TGA, zeta potential and XRF. The techniques verified the effect of thermal treatment on samples structures and the enhancement of negative charge. Both raw and thermally-activated materials applied in batch kinetic experiments, and found to be efficient adsorbents in their raw forms, since Pal and Sep achieved 60 and 80% NH4+-N removal respectively within 20 min of contact for initial NH4+-N concentration of 4 mg/L. Similar removal rates were gained for other concentrations representative of contaminated aquifers that were examined, ranging from 1 mg/L to 8 mg/L. Results for the modified T-Pal and T-Sep minerals showed up to 20% higher removal rate. Saturation tests indicated the positive effect of thermal treatment on the minerals since T-Pal and T-Sep removal efficiency reached 85% and remained stable for 24 h. However, competitive ions in real water samples can influence the NH4+-N removal efficiency of the examined samples. In all cases, the Freundlich isotherm and pseudo-second kinetic models showed better fitted all examined samples thus indicating heterogeneous chemisorption.

Raw and modified fibrous clay minerals palygorskite (Pal) and sepiolite (Sep) were tested for their ability to remove ammonium from ammonium polluted water. Palygorskite and sepiolite underwent thermal treatment at 400°C (T-Pal and T-Sep respectively). Raw and thermally treated samples were characterized using XRD, SEM, BET, FTIR, TGA, zeta potential, and XRF. The techniques verified the effect of thermal treatment on sample structures and the enhancement of negative charge. Both raw and thermally activated materials were applied in batch kinetic experiments, and found to be efficient adsorbents in their raw forms, since Pal and Sep achieved 60 and 80% NH

Pomegranate residues (PRs) (i.e. the solid residues remaining after juice extraction), generated currently in abundance in Greece, contain a variety of carbon sources and therefore can be regarded as a potential feedstock for chemical and biotechnological processes rather than as waste materials. In the current project, the polysaccharides contained in PRs were extracted and hydrolyzed in a one-step process without the use of chemical reagents and the resulting broth was used as substrate in biotechnological applications, including ethanol and single cell oil (SCO) production. The yeasts Meyerozyma guilliermondii, Scheffersomyces coipomoensis, Sugiyamaella paludigena and especially Saccharomyces cerevisiae, were able to efficiently convert PR derived reducing sugars into bioethanol. Ethanol production under anaerobic conditions ranged from 3.6 to 12.5 g/L. In addition, the oleaginous yeasts Lipomyces lipofer and Yarrowia lipolytica as well as M. guilliermondii, S. coipomoensis and S. paludigena were tested for their ability to accumulate lipids suitable as feedstock for biodiesel production. Lipids were accumulated at concentrations up to 18% and were rich in palmitic acid (C16:0) and oleic acid (C18:1). Finally, the oleaginous fungus Cunnichamella echinulata was cultivated on PR based solid substrates for γ-linolenic acid (GLA) production. The fermented bio-products (i.e. fermented substrate plus fungal mycelia) contained up to 4.8 mg GLA/g of dry weight. Phenolic removal (up to 30%) was achieved by several of the above mentioned microorganisms, including C. echinulata, L. lipofer, M. guilliermondii, S. paludigena and Y. lipolytica. We conclude that PRs can be used as a raw material for microbial growth, ethanol and SCO production, which is of economic and environmental importance.

A mixed cyanobacterial-mixotrophic algal population, dominated by the filamentous cyanobacterium Leptolyngbya sp. and the microalga Ochromonas (which contributed to the total photosynthetic population with rates of less than 5%), was studied under non-aseptic conditions for its efficiency to remove organic and inorganic compounds from different types of wastes/wastewaters while simultaneously producing lipids. Second cheese whey, poplar sawdust, and grass hydrolysates were used in lab-scale experiments, in photobioreactors that operated under aerobic conditions with different initial nutrient (C, N and P) concentrations. Nutrient removal rates, biomass productivity, and the maximum oil production rates were determined. The highest lipid production was achieved using the biologically treated dairy effluent (up to 14.8% oil in dry biomass corresponding to 124 mg L−1) which also led to high nutrient removal rates (up to 94%). Lipids synthesized by the microbial consortium contained high percentages of saturated and mono-unsaturated fatty acids (up to 75% in total lipids) for all the substrates tested, which implies that the produced biomass may be harnessed as a source of biodiesel.

Raw, thermal- and acid-treated palygorskite (Pal/ T-Pal/ H-Pal ) and sepiolite (Sep/ T-Sep/ H-Sep) were applied to adsorb NO 3 − -N from aqueous solutions. A series of batch kinetic experiments was conducted on NO 3 − -N removal while investigating the effects of initial pollutant concentrations, adsorbent dosages and solution pH. Adsorbent dosages of 4.0 g resulted in NO 3 − -N removal within 20 min. Removal capacities of raw Pal and Sep were examined in solutions with 15–100 mg NO 3 − -N/L. Acid treatment enhanced the capacity of Pal and Sep to remove initial concentrations of 15 mg NO 3 − -N/L from 0.15 and 0.10 mg/g to 0.28 and 0.32 mg/g, respectively, whereas thermal treatment did not improve NO 3 − -N removal capacities of either mineral. The NO 3 − -N adsorption was better expressed by Langmuir isotherm and pseudo-first order kinetic model, except from Pal sample where Freundlich and pseudo-second order kinetic presented better fit. Saturation tests showed that all adsorbents were saturated within 24 h, while desorption tests showed that most nitrate was released within 12 h. Despite their rapid nitrate release, raw and modified Pal and Sep were applied as effective nitrogen fertilizers in 40-day hydroponic cultivations of lettuce seedlings. Both minerals proved to be effective N fertilizers for hydroponic lettuce cultivations. Raw Pal and Sep potentially boosted N uptake more than the modified clay samples. Pal fertilizers significantly improved root growth and Sep fertilizers enhanced shoot height.

Pomegranate residues (PRs), the solid residues comprising peels and seeds after juice extraction, are generated in abundance in Greece and contain a variety of carbon sources. Therefore, these residues can be regarded as a potential feedstock for chemical and biotechnological processes. The polysaccharides contained in PRs were extracted and hydrolyzed in a one-step process (not involving the use of chemical reagents), and the resulting broth was used as substrate in biotechnological applications, including ethanol and single cell oil (SCO) production. The yeasts Meyerozyma guilliermondii, Scheffersomyces coipomoensis, Sugiyamaella paludigena and especially Saccharomyces cerevisiae were able to efficiently convert reducing sugars derived from PRs into bioethanol. Ethanol production in static cultures (ensuring nearly anaerobic conditions) ranged from 3.6 to 12.5 g/L. In addition, the oleaginous yeasts Lipomyces lipofer and Yarrowia lipolytica as well as M. guilliermondii, S. coipomoensis and S. paludigena were tested for their ability to produce lipids suitable as feedstock for biodiesel production. Lipids were accumulated at concentrations up to 18% and were rich in palmitic and oleic acids. Finally, the oleaginous fungus Cunnichamella echinulata was cultivated on PR-based solid substrates for γ-linolenic acid (GLA) production. The fermented bio-products (i.e. fermented substrate plus fungal mycelia) contained up to 4.8 mg GLA/g of dry weight. Phenolic removal (up to 30%) was achieved by several of the above-mentioned microorganisms, including C. echinulata, L. lipofer, M. guilliermondii, S. paludigena and Y. lipolytica. In conclusion, the findings of this study demonstrate that PRs can be used as raw material for microbial growth, ethanol and SCO production, which is of economic and environmental importance.

The use of Constructed Wetlands (CWs) has been nowadays expanded from municipal to industrial and agro-industrial wastewaters. The main limitations of CWs remain the relatively high area requirements compared to mechanical treatment technologies and the potential occurrence of the clogging phenomenon. This study presents the findings of an innovative CW design where novel materials were used. Four pilot-scale CW units were designed, built and operated for two years. Each unit consisted of two compartments, the first of which (two thirds of the total unit length) contained either fine gravel (in two units) or random type high density polyethylene (HDPE) (in the other two units). This plastic media type was tested in a CW system for the first time. The second compartment of all four units contained natural zeolite. Two units (one with fine gravel and one with HDPE) were planted with common reeds, while the other two were kept unplanted. Second cheese whey was introduced into the units, which were operated under hydraulic residence times (HRT) of 2 and 4 days. After a two-year operation and monitoring period, pollutant removal rates were approximately 80%, 75% and 90% for COD, ammonium and ortho-phosphate, respectively, while temperature and HRT had no significant effect on pollutant removal. CWs containing the plastic media achieved the same removal rates as those containing gravel, despite receiving three times higher hydraulic surface loads (0.08 m/d) and four times higher organic surface loads (620 g/m2/d). This reveals that the use of HDPE plastic media could reduce CW surface area requirements by 75%.

Combining wastewater treatment with biodiesel production can greatly reduce the cost of environmentally friendly technologies. In this work wastewaters of high environmental importance originating from raisin and wine industries were employed as substrates for a mixed cyanobacterial/algal cultivation system dominated by the filamentous cyanobacterium Leptolyngbya sp. The mixotrophic microalga Ochromonas contributed to less than 5% of the total photosynthetic population and grazed on broken Leptolyngbya trichomes. Satisfactory lipid yields and removal of nutrients and chemical oxygen demand (COD) were observed when raisin or winery wastewaters were used separately as substrates. However, exceptional removal rates were recorded in blends of the above-mentioned wastewaters (i.e., 92.8%, 78.1% and 99% for COD, total nitrogen and phosphate, respectively), while the biomass produced contained around 13% lipids (w/w) on a dry weight basis. The ratio of saturated/mono-unsaturated fatty acids in this lipid reached 85%, making this system suitable for biodiesel production. The proposed system can effectively approach a technology that integrates wastewater treatment with simultaneous biodiesel production.

The efficiency of natural zeolite to treat second cheese whey (SCW) and remove ammonium from artificial wastewater (AWW) was examined. Since zeolite has been reported to improve nitrogen availability in soils, its effect on wheat plant growth was also examined. Continuing a previous study using batch reactors, results are presented concerning experiments in fixed-bed columns under continuous operation. Results from the continuous flow column experiments using AWW and zeolite (2.0&ndash, 2.8 mm) indicated that low flow rates (4 mL/min and 8 mL/min) did not significantly affect zeolite adsorption ability, while maximum zeolite adsorption capacity reached 15.30 mg NH4+-N/g. Finally, the effect of zeolite saturated with NH4+-N on plant growth was examined. The application of saturated zeolite affected significantly wheat plant growth and resulted in faster growth and higher biomass production.

Food processing consumes high volumes of water, making agro-industries the third biggest industrial user of water after oil refineries, primary metals and chemicals industries [...]

In this study, natural zeolite with maximum adsorption capacity of 3.59 mg g−1 was used for the simultaneous removal of ammonium nitrogen (NH4+-N), dissolved chemical oxygen demand (d-COD) and color from raw sanitary landfill leachate (SLL). Saturation, desorption and regeneration tests of zeolite were performed. Optimum adsorption conditions were found for particle size 0.930 µm, stirring rate of 1.18 m s−1, zeolite dosage of 133 g L−1 and pH 8. NH4+-N removal efficiency reached 51.63 ± 0.80% within 2.5 min of contact. NH4+-N adsorption follows mostly the linear pseudo-second order model, with intra-particle diffusion. NH4+-N desorption follows the linear pseudo-second order model. Adsorption data fitted to the Temkin Isotherm in linear and nonlinear forms. Saturation tests showed that zeolite can be efficiently used in three successive adsorption cycles. NH4+-N release from the saturated zeolite was not completely reversible, suggesting that the zeolite may be used as slow ΝΗ4+-Ν releasing fertilizer and an attractive low cost material for the treatment of SLL. NH4+-N removal with the regenerated zeolite exceeded 40% of the initial concentration in the fluid within 2.5 min. SEM analysis showed significant changes through saturation and regeneration. XPS revealed that adsorption of ΝΗ4+-Ν to the zeolite was accompanied by ion exchange.

In the present study the whole slurry obtained after different pretreatment methods applied on sunflower straw (SS) biomass, was used for biological production of hydrogen (BHP) and ethanol (BEP). BHP from pretreated SS was studied in batch experiments using mixed anaerobic sludge, via simultaneous saccharification and fermentation (SSF), while for BEP, SSF was carried out using the xylose – fermenting yeast Pichia stipitis. The experimental results obtained showed that for BHP, alkaline pretreatment with 20 g NaOH/100 gTS was optimal, leading to the highest hydrogen yield of 155.3 ± 6.5 L/kg TS. This yield was 52.5 times higher than the respective of raw SS (2.9 ± 0.0 LH2/kgTS) without enzyme addition. Pretreatment with the same chemical loadings of HCl or H2SO4 resulted in the lowest BHP yields, due to the generation of inhibitory compounds. Although pretreatment with 20 g H2SO4/100 gTS also caused inhibition of P. stipitis giving the lowest BEP yield, pretreatment with 20 g HCl/100 gTS led to the highest BEP yield of 104.78 ± 0.08 mg ethanol/gTS, indicating the varying sensitivity of different microbial species to the inhibitory compounds that are generated during pretreatment.

This work studied heterotrophic denitrification in packed-bed reactors using sugar as electron donor and carbon source. Two pilot-scale bio-filters, loaded with different types and sizes of support media, were operated under sequencing batch (SBR) mode with recirculation. The materials used were silicic gravel placed in two layers (diameter 2.41 and 4.03 mm) within the first filter (R1 – multilayer), and hollow plastic tubes (diameter 1.6 cm) within the second filter (R2 – monolayer). Feed NO 3 − -N concentrations ranged between 20 and 400 mg/L, while the C/N ratio was kept constant at 13.5. Higher denitrification rates (4.06–8.76 kg N/(m 3 d)) and total sugar biodegradation were observed in bio-filter R1 than in R2. However, carbon residues were observed in the treated water of bio-filter R1 for feed concentrations above 70 mgNO 3 − -N/L. Bio-filter R1 was then used to study the effect of C/N ratio on its performance. Experiments showed that a decrease of the C/N ratio from 13.5 to 6.25 resulted in lower carbon residue in the treated water and high denitrification rates (3.21–6.64 kgN/(m 3 d)), however, significant NO 2 − -N accumulation was observed. Further reduction of the C/N ratio (i.e., 5.48 and 4.71) resulted in filter malfunction as insufficient removal of NO 3 − -N was achieved. Results suggest that under the more favourable conditions of C/N:13.5 and silicic gravel support material, satisfactory NO 3 − -N and COD removal could be achieved for feed concentrations up to 60 mgNO 3 − -N/L at a cost of 0.019 €/KgN or 1.13 × 10 −3 €/m 3 , which is much lower than ever reported in the literature and confirms the economic viability of the process. To describe the heterotrophic denitrification process, a mathematical model of microbial growth on nitrate and nitrite treated as substitutable substrates and sugar as the carbon source is proposed. Model simulations could be used as a guide for the optimum design and operation of water treatment systems for nitrate removal.

In this work table olive processing wastewaters (TOPW) were treated by aerobic biological processes using indigenous microorganisms originating from TOPW, as well as the combination of two successive steps, i.e. aerobic biological treatment followed by electrochemical oxidation over a boron-doped diamond anode. In the single aerobic biological processes, experiments in suspended and attached growth reactors (trickling filters) were carried out using different TOPW feed concentrations of 5500 ± 350, 7500 ± 650 and 15,000 ± 1050 mg dissolved COD L−1. Two different operating modes were used to investigate the optimum performance of the filter, i.e. batch and SBR with recirculation. The latter mode with recirculation of 0.5 L min−1 led to high removal rates of dissolved COD and total phenolic compounds, up to 96.5% and 64.5%, respectively, for the initial COD concentration of 7500 mg dissolved COD L−1. Depending on the type and operating conditions of the bioreactors, residual COD ranged between a few hundred and a few thousand mg L−1, while decolorization could not be achieved even under the most favorable conditions. A biologically treated effluent with residual dissolved COD of 5100 mg L−1 was completely mineralized and decolorized at 187.5 mA cm−2 applied current density; complete removal of COD, color and total phenolic compounds was achieved in 180–240 min, 30–60 min and 30 min of electrochemical oxidation, respectively. Lower treatment times and current densities were needed to polish effluents with lower organic loads.

The efficiency of natural zeolite to remove ammonium from artificial wastewater (ammonium aqueous solutions) and to treat second cheese whey was examined, aiming to recover nitrogen nutrients that can be used for further applications, such as slow-release fertilizers. Sorption experiments were performed using artificial wastewater and zeolite of different granulometries (i.e., 0.71&ndash, 1.0, 1.8&ndash, 2.0, 2.0&ndash, 2.8, 2.8&ndash, 4.0, and 4.0&ndash, 5.0 mm). The granulometry of the zeolite had no significant effect on its ability to absorb ammonium. Nevertheless, smaller particles (0.71&ndash, 1.0 mm) exhibited quicker NH4+-N adsorption rates of up to 93.0% in the first 10 min. Maximum ammonium removal efficiency by the zeolite was achieved at ammonium concentrations ranging from 10 to 80 mg/L. Kinetic experiments revealed that chemisorption is the mechanism behind the adsorption process of ammonium on zeolite, while the Freundlich isotherm model fitted the experimental data well. Column sorption experiments under batch operating mode were performed using artificial wastewater and second cheese whey. Column experiments with artificial wastewater showed high NH4+-N removal rates (over 96% in the first 120 min) for all granulometries and initial NH4+-N concentrations tested (200 and 5000 mg/L). Column experiments with second cheese whey revealed that natural zeolite can remove significant organic loads (up to 40%, 14.53 mg COD/g of zeolite) and NH4+-N (about 99%). For PO43&minus, P, the zeolite appeared to saturate after day 1 of the experiments at a removal capacity of 0.15 mg P/g of zeolite. Desorption experiments with water resulted in low NH4+-N and PO43&minus, P desorption rates indicating that the zeolite could be used as a substrate for slow nitrogen release in soils.

BACKROUND Recently the utilization of microalgae for biological nutrient and organic load removal from industrial wastewater streams has been of great research interest. This present research aimed to develop a biological (algal) second cheese whey wastewater (SCWW) treatment system able to generate renewable energy in the form of biodiesel while simultaneously removing polluting nutrients and chemical oxygen demand (COD). RESULTS Aerobically-treated SCWW was diluted in water (dilution factor from 0.05 to 0.35) and evaluated as a substrate for Choricystis-like algal growth under photoheterotrophic conditions. Specifically, the algal culture was studied under non-aseptic conditions for its ability to remove COD, nitrogen, and phosphorous from SCWW and to produce biodiesel. At the end of treatment the pollutant load of COD, TN and PO43− was reduced by up to 92.3%, 97.3%, and 99.7%, respectively. The lipid content of the algal biomass ranged from 9.2 to 13.4%, which corresponds with an oil production of 60.8–119.5 mg L−1. The proportions of saturated and mono-unsaturated fatty acids in the lipids produced reached 79%, thus making the system suitable for biodiesel production. CONCLUSIONS A well-adapted Choricystis-like consortium could be efficiently used to treat SCWW while the biomass produced may be harnessed as a source of biodiesel. © 2015 Society of Chemical Industry

The present study aimed at developing an integrated mathematical model for the composting process of olive mill waste. The multi-component model was developed to simulate the composting of three-phase olive mill solid waste with olive leaves and different materials as bulking agents. The modeling system included heat transfer, organic substrate degradation, oxygen consumption, carbon dioxide production, water content change, and biological processes. First-order kinetics were used to describe the hydrolysis of insoluble organic matter, followed by formation of biomass. Microbial biomass growth was modeled with a double-substrate limitation by hydrolyzed available organic substrate and oxygen using Monod kinetics. The inhibitory factors of temperature and moisture content were included in the system. The production and consumption of nitrogen and phosphorous were also included in the model. In order to evaluate the kinetic parameters, and to validate the model, six pilot-scale composting experiments in controlled laboratory conditions were used. Low values of hydrolysis rates were observed (0.002841/d) coinciding with the high cellulose and lignin content of the composting materials used. Model simulations were in good agreement with the experimental results. Sensitivity analysis was performed and the modeling efficiency was determined to further evaluate the model predictions. Results revealed that oxygen simulations were more sensitive on the input parameters of the model compared to those of water, temperature and insoluble organic matter. Finally, the Nash and Sutcliff index (E), showed that the experimental data of insoluble organic matter (E>0.909) and temperature (E>0.678) were better simulated than those of water.

In this study, various pretreatment methods, such as thermal (24 h at 80 °C; 1 h at 120 °C), alkaline (2–20 g ΝaΟΗ/100 g TS, 24 h at 80 °C) and acid (2–20 g Η2SO4/100 g TS, 1 h at 120 οC; 2–20 g Η3PO4/100 g TS, 1 h at 120 °C; 2–20 g HCl/100 g TS, 1 h at 120 °C), were applied on sunflower straw biomass and the effect of each pretreatment method on the fractionation of the lignocellulosic content was evaluated. Experiments showed that pretreatment with the acids led to higher hemicellulose solubilization, while lignin degradation was achieved when the sunflower was treated with NaOH. Higher acids concentration led to higher solubilization of hemicellulose and higher concentrations of released furaldehydes (5-hydroxymethylfurfural and furfural) and aliphatic acids (i.e. formic and acetic acid). On the contrary, the higher the NaOH concentration, the higher was the phenolics concentration observed. Scanning electron microscopy images revealed a change in morphology after different pretreatment methods, compared to the raw substrate. Thus, disruption of the outer layers and removal of mass from the initial connected structure were observed, for all pretreated feedstocks. Complete analysis of the liquid fractions obtained after pretreatment, led to the estimation of the ratio of sum of soluble sugars concentration to the sum of inhibitors concentration (Σ(soluble sugars)/Σ(inhibitors)), which characterizes the fermentability of the sunflower straw hydrolysates.

Composting is considered a viable solution for olive mill waste. Among others, composting duration, bulking agents and their ratios are crucial factors that determine the quality of the final product. To examine optimal ratios and bulking agent types (i.e., olive leaves, rice husk, sawdust, wood shavings and chromium treated reeds), six parallel compost experiments were conducted with olive pomace. Experimental results indicate that all final composts presented similar physicochemical characteristics, while their values met EU legislation limits for soil amendments. Furthermore, the germination index (GI) in all final composts was above 100%, indicating the absence of any phytotoxic effect. Genotoxic and cytotoxic evaluation of the composts revealed that all initial mixtures presented cytotoxic effects. Genotoxic and cytotoxic effects were more intense during the thermophilic phase (all compost mixtures presented both genotoxic and cytotoxic effects). The majority of mature composts (102 days) did not have any genotoxic and cytotoxic effect. However, genotoxic and cytotoxic effects could appear if compost is not mature or specific materials (i.e., olive pomace and rice husk) have been used in excess. This work points out the significance of genotoxic and cytotoxic evaluation in olive mill waste compost, thus, indicating that similar evaluations should be performed for other compost materials deriving from agro-industrial and municipal wastes. Therefore, the revision of EU regulations is proposed to include genotoxic and cytotoxic evaluation of composts that enter the human food chain.

BACKGROUND One of the main components of dairy wastewaters is cheese whey. Although different technologies have been used extensively in the past for cheese-whey treatment, constructed wetlands (CWs) applications are limited. Furthermore, the effect of crucial operational parameters (e.g. temperature, pollutant loading rate) have not been thoroughly studied. Having this in mind, two horizontal subsurface flow pilot-scale CW units (one planted and one unplanted) were used to treat secondary cheese whey, in order to examine the effect of different chemical oxygen demand (COD) influent concentrations (1200 to 7200 mg L−1), hydraulic residence times (8, 4, 2 and 1 day) and temperature (2.4 to 32.9 °C). RESULTS During a 2-year operating period both pilot-scale units successfully removed organic matter, with COD removal efficiencies recorded at 91% and 77.2% for the planted and the unplanted unit, respectively. Hydraulic residence time affected COD removal efficiency only when limited to 1 day. Temperature significantly affected COD removal only in the unplanted unit. CONCLUSIONS Constructed wetlands could successfully treat secondary cheese whey and provide COD effluent concentrations below EU legislation, when hydraulic residence time is above 2 days and COD influent concentration ranges from 1200 to 3500 mg L−1. © 2015 Society of Chemical Industry

An olive mill's existing evaporation pond was separated into five cells and transformed into a free water surface constructed wetland. The constructed wetland was used as a post-treatment stage for olive mill wastewater (OMW). Wastewater was previously treated by an aerobic trickling filter. The influent concentrations in the constructed wetland were 27400 mg.L-1, 4800 mg.L-1, 105 mg.L-1 and 770 mg.L-1 for COD, phenols, ortho-phosphate and TKN, respectively. Despite the rather high influent concentrations, the performance of the constructed wetland was very good since after the 60-day start-up operation period it achieved removal rates of about 94%, 95%, 95% and 98% for COD, phenols, ortho-phosphate and TKN, respectively. The major pollutant removal processes can be attributed to both biological processes occurring in the wetland and photo-oxidation. Laboratory-scale experiments with OMW from fifth cell of the wetland revealed that the net contribution of photo-oxidation after 112 hours of simulated solar radiation at 765 W/m2 (i.e. about 38 days of sunlight irradiation) was 18% and 31% removal for COD and phenols, respectively. In the constructed wetland, the total removal reached 81% and 86% for COD and phenols, respectively, for the same time period (38 days).

In the present study, indigenous microorganisms from industrial sludge were used to reduce the activity of Cr(VI). Molasses, a by-product of sugar processing, was selected as the carbon source (instead of sugar used in a previous work) as it is a low-cost energy source for bioprocesses. Initially, experiments were carried out in suspended growth batch reactors for Cr(VI) concentrations of 1.5–110 mg/L. The time required for complete Cr(VI) reduction increased with initial Cr(VI) concentration. Initial molasses concentration was also found to influence the Cr(VI) reduction rate. The optimal concentration for all initial Cr(VI) concentrations tested was 0.8 gC/L. Experiments were also carried out in packed-bed reactors. Three different operating modes were used to investigate the optimal performance and efficiency of the filter, i.e. batch, continuous and SBR with recirculation. The latter mode with a recirculation rate of 0.5 L/min lead to significantly high Cr(VI) reduction rates (up to 135 g/m 2 d). The results of this work were compared with those of a similar work using sugar as the carbon source and indicate that molasses could prove a feasible technological solution to a serious environmental problem.

Due to their simplicity and low operation cost, constructed wetlands are becoming more prevalent in wastewater treatment all over the world. Their range of applications is no longer limited to municipal wastewater but has expanded to the treatment of heavily polluted wastewaters such as agro-industrial effluents. This paper provides a comprehensive literature review of the application of constructed wetlands in treating a variety of agro-industrial wastewaters, and discusses pollutant surface loads and the role of constructed wetland type, prior-treatment stages and plant species in pollutant removal efficiency. Results indicate that constructed wetlands can tolerate high pollutant loads and toxic substances without losing their removal ability, thus these systems are very effective bio-reactors even in hostile environments. Additionally, the review outlines issues that could improve pollutant treatment efficiency and proposes design and operation suggestions such as suitable vegetation, porous media and constructed wetland plain view. Finally, a decision tree for designing constructed wetlands treating agro-industrial wastewaters provides an initial design tool for scientists and engineers.

Excessive use of nitrogenous fertilizers has led to increased nitrate concentrations in groundwater that pose a threat to human health, via nitrate-contaminated potable water, and contribute to eutrophication. The elimination of nitrate from water systems has been thoroughly examined; however, unconventional and low-cost technologies are greatly needed. Clays and clay minerals are widely-used for environmental applications, mostly due to their non-toxicity, worldwide abundance, low cost and physicochemical properties (high surface area, ion exchange capacity, high sorption and catalytic properties). Most are used for the degradation of cationic pollutants, nevertheless, they can be equally efficient at anionic decontamination, depending on the modification process they have undergone, or the materials they are combined with. This review aims to assemble the available literature research on the application of clays and clay minerals as well as the mechanisms that lead to successful removal of nitrate from water. The main characteristics of clays and clay minerals in nitrate uptake are evaluated and the known shortcomings of their application discussed, leading to suggestions for further research.

Various pretreatment methods, such as thermal, alkaline and acid, were applied on grass lawn (GL) waste and the effect of each pretreatment method on the Biochemical Methane Potential was evaluated for two options, namely using the whole slurry resulting from pretreatment or the separate solid and liquid fractions obtained. In addition, the effect of each pretreatment on carbohydrate solubilization and lignocellulossic content fractionation (to cellulose, hemicellulose, lignin) was also evaluated. The experimental results showed that the methane yield was enhanced with alkaline pretreatment and, the higher the NaOH concentration (20 g/100 gTotal Solids (TS)), the higher was the methane yield observed (427.07 L CH4/kg Volatile Solids (VS), which was almost 25.7% higher than the BMP of the untreated GL). Comparing the BMP obtained under the two options, i.e., that of the whole pretreatment slurry with the sum of the BMPs of both fractions, it was found that direct anaerobic digestion without separation of the pretreated biomass was favored, in almost all cases. A preliminary energy balance and economic assessment indicated that the process could be sustainable, leading to a positive net heat energy only when using a more concentrated pretreated slurry (i.e., 20% organic loading), or when applying NaOH pretreatment at a lower chemical loading.

The distribution, mobility and availability of metals in the environment depend not only on their total concentration but also on their formations and bounds with the soil. Hexavalent chromium is a very toxic, metal compound, frequently found in polluted industrial wastewaters, and causes serious environmental problems. The potential application of constructed wetlands in the treatment of chromium bearing wastewaters has been reported recently. This paper reviews research on constructed wetlands treating chromium polluted wastewaters, and focuses on several design and operational parameters. The review highlights the effect of vegetation type, hydraulic residence time and porous media type on wetland performance. Constructed wetlands have been proved to be rather efficient at treating chromium containing wastewaters.

BACKGROUND Second cheese whey is a strong organic and saline effluent whose characterization and treatment have not been sufficiently addressed. RESULTS Indigenous microorganisms from second cheese whey were isolated for its aerobic biological degradation. Experiments in suspended and attached growth reactors (lab and pilot scale) were carried out using different feed whey concentrations. These concentrations corresponded to three different dilutions with tap water, using 25%, 50% and 75% whey (concentrations C25, C50 and C75, respectively), as well as without dilution (100% whey, C100). The maximum degradation rate of the organic load obtained in the suspended growth reactors was achieved for the concentration C100 (10.06 g d-COD L−1 day−1). Degradation was more rapid (26.3 g d-COD L−1 day−1) in a lab-scale packed bed reactor with recirculation and concentration C75. Experiments in a pilot-scale reactor with recirculation were also performed with high degradation rates (6.41 g d-COD L−1 day−1) under various environmental conditions. The long-term degradation efficiency (12 month operation period) and the effect of environmental and operating conditions on filter performance were studied. CONCLUSIONS Aerobic biological treatment at the proposed pilot-scale filter proved to be a sufficient method. The simplicity of the installation provides an effective solution to a serious environmental and social problem. © 2014 Society of Chemical Industry

BACKGROUND Many physicochemical, biological and disposal technologies have been suggested for the effective treatment of olive mill wastewaters (OMW), wastes with very high organic content, non-readily degradable content and phytotoxic characteristics, and considered one of the major polluting agents in Mediterranean countries from agricultural activities. RESULTS The treatment of OMW by means of coagulation–flocculation using various inorganic materials (poly-aluminum chloride – PAC, aluminum sulphate) and organic poly-electrolytes (anionic polyacrylamide – Flocan 23–20, anionic polyelectrolyte – Praestol 2240) was investigated in this study. This technology was examined as a single stage treatment of two different (in composition) olive mill wastewaters, and a second treatment stage following aerobic biological treatment in a biofilter. Treatment effectiveness was assessed through dissolved chemical oxygen demand (COD), total phenolic content (TP), total solids (TS), total suspended solids (TSS) removal, and zeta potential. Results revealed that PAC presents better and more stable treatment efficiency than aluminum sulphate. The optimum electrolyte concentration varies for the wastewaters used depending on their composition and the electrolyte's chemical structure. An economic analysis was performed taking coagulant and flocculant costs into account. CONCLUSIONS The treatment of OMW by means of coagulation–flocculation using various inorganic materials (poly-aluminum chloride – PAC, aluminum sulphate) and organic poly-electrolytes (anionic polyacrylamide – Flocan 23–20, anionic polyelectrolyte – Praestol 2240) was investigated in this study. This technology was examined as a single stage treatment of two different (in composition) olive mill wastewaters, and a second treatment stage following aerobic biological treatment in a biofilter. Treatment effectiveness was assessed through dissolved chemical oxygen demand (COD), total phenolic content (TP), total solids (TS), total suspended solids (TSS) removal, and zeta potential. Results revealed that PAC presents better and more stable treatment efficiency than aluminum sulphate. The optimum electrolyte concentration varies for the wastewaters used depending on their composition and the electrolyte's chemical structure. An economic analysis was performed taking coagulant and flocculant costs into accountThe use of combinations of electrolytes and polyelectrolytes was effective at reducing all parameters analysed. Optimum treatment and economic performance was observed in the case of combined biological and physicochemical treatment, which achieved COD, TP, TS and TSS removal rates of 65.5%, 66%, 71% and 99.2%, respectively; this corresponds to 0.36 €/ m3 of treated OMW. © 2013 Society of Chemical Industry

Olive mill wastes exacerbate environmental problems in Mediterranean countries. These wastes are highly phytotoxic and contain phenolic compounds, lipids and organic acids. They also contain high percentages of organic matter and a vast range of plant nutrients that could be reused as fertilizers for sustainable agricultural practices. In this paper, recent research on composting wastes of 2-phase and 3-phase olive mills is reviewed, concentrating on factors affecting composting such as bulking agents, aeration strategy, physicochemical characteristics (duration of the thermophilic phase, moisture content, organic matter, volatile solids, total organic carbon, water soluble carbon, total nitrogen, total phosphorus, potassium, C/N ratio, phenols and the humification process), and phytotoxicity. The review highlights the effects of composting operational factors (bulking agent, additives, and aeration strategy) on the physicochemical characteristics of the final compost, and the production of a good quality soil amender or fertilizer.

Ammonium, and trace metals such as iron and manganese are common inorganic pollutants present in waters. Several surface and groundwaters contain natural or increased concentrations of these pollutants that are observed either isolated or in pairs, or all three together. Although several processes have been established for the biological removal of one of the above-mentioned pollutants, only recently have important studies been performed on the efficient and cost-effective simultaneous biological removal of two or more substances. This paper reviews the variety of full- and pilot-scale biological filters that have been used for combined or simultaneous biological removal, as well as factors and conditions that were found to affect the process. The main results regarding research progress on combined or simultaneous biological removal are evaluated. Finally, the kinetic models and simulation approaches used are discussed. © 2013 Society of Chemical Industry

The biological treatment of olive mill waste has gained attention over recent years as it can achieve high removal efficiencies at relatively low cost. Several studies have proved that attached growth biological systems are efficient at treating olive mill wastewater as their high biomass concentration can tolerate substantial organic loadings without the appearance of toxic effects. Attached growth systems can remove the majority of the organic load; however, due to the extremely high organic load of olive mill wastewater, a posttreatment stage is imperative. Constructed wetlands are often currently used as a polishing treatment stage for olive mill wastewater. Furthermore, olive mills also produce significant quantities of solid residues that have proved to be excellent materials for composting. This chapter presents an integrated approach for the treatment of olive mill wastewater and solid residue that uses only biological treatments (i.e., trickling filters, constructed wetlands, and composting).

Although olive mill wastes (OMW) are characterized as phytotoxic and considered a threat to the environment, they also contain substances (e.g., organic matter, minerals, and nutrients) that are essential for crop growth. For this reason, composting has been deemed a rather attractive valorization method for OMW. A vast number of applications and experiments concerning OMW composting have been conducted using various operational parameters (e.g., bulking agents, aeration strategies, and C/N ratios). This chapter presents a brief literature overview on this topic, as well as the design and operation of two OMW case studies (pilot-scale and full-scale approaches). Experimental results in pilot- and full-scale units revealed that composts deriving from OMW have excellent physicochemical characteristics with no phytotoxic effects. However, genotoxic and cytotoxic effects should be evaluated before using these composts for agricultural purposes. Finally, this chapter also presents an integrated mathematical model of the OMW composting process that describes both physicochemical and biological processes.

The production of table olives is a significant economic activity in Mediterranean countries. Table olive processing generates large volumes of rinsing water that are characterized by high organic matter and phenol contents. Due to these characteristics, a combination of more than one technology is imperative to ensure efficient treatment with low operational cost. Previously, biological filters were combined with electrooxidation to treat table olive washing water. Although this combination was successful in reducing pollutant loads, its cost could be further reduced. Constructed wetlands could be an eligible treatment method for integrated table olive washing water treatment as they have proved tolerant to high organic matter and phenol loads. Two pilot-scale horizontal subsurface constructed wetlands, one planted and one unplanted, were combined with a biological filter and electrooxidation over a boron-doped diamond anode to treat table olive washing water. In the biological filter inlet, chemical oxygen demand (COD) concentrations ranged from 5500 to 15,000 mg/L, while mean COD influent concentration in the constructed wetlands was 2800 mg/L. The wetlands proved to be an efficient intermediate treatment stage, since COD removal levels for the planted unit reached 99 % (mean 70 %), while the unplanted unit presented removal rates of around 65 %. Moreover, the concentration of phenols in the effluent was typically below 100 mg/L. The integrated trickling filter-constructed wetland-electrooxidation treatment system examined here could mineralize and decolorize table olive washing water and fully remove its phenolic content.

The composting of olive leaves and olive pomace from a three-phase olive mill was tested as a method for solid waste reuse. The process was carried out using a compost windrow and mixing olive leaves and pomace at a ratio of 1:2. Compost was retained in the windrow for 60 days during which thermophilic temperatures developed for the first 40 days. The compost was then placed into a closed area to mature for another 60 days. The final product proved to be high quality amendment with C/N 27.1 and high nutrient concentrations (N, 1.79%; P, 0.17%; K, 4.97%; Na, 2.8%). Mature compost presented the highest germination index (198%) reported to date, as the germination index in the majority of previous studies is under 80%. Furthermore, tests revealed that addition of 31.5 tons of compost per ha, could increase lettuce yield by 145%.

Pilot-scale constructed wetlands (CW) were constructed and operated to treat pre-treated olive mill wastewater. Pilot-scale units comprising three identical series with four pilot-scale vertical flow CWs were operated for one harvest season in a Greek olive mill plant. The pilot-scale CWs were filled with various porous media (i.e., cobble, gravel, and sand) of different gradations. Two series of pilot-scale units were planted with common reeds and the third (control) was unplanted. Mean influent concentrations were 14,120 mg/L, 2841 mg/L, 95 mg/L, 123 mg/L and 506 mg/L for COD, phenols, ortho-phosphate, ammonia and TKN, respectively. Despite the rather high influent concentrations, the performance of the CW units was very effective since it achieved removals of about 70%, 70%, 75% and 87% for COD, phenols, TKN and ortho-phosphate, respectively. COD, phenol and TKN removal seems to be significantly higher in the planted series, while ortho-phosphate removal shows no significant differences among the three series. Temperature and pollutant surface load seem to affect the removal efficiency of all pollutants. Compared to previous studies, pollutant surface loads applied here were higher (by one or two orders of magnitude). Even though high removal efficiencies were achieved, effluent pollutant concentrations remained high, thus preventing their use for irrigation or immediate disposal into the environment.

The use of cyanobacteria in biological wastewater treatment technologies can greatly reduce operation costs by combining wastewater bioremediation and production of lipid suitable as biodiesel feedstock. In this work, an attached growth system was employed to achieve the above-mentioned dual objective using a mixed microbial culture dominated by Leptolyngbya and Limnothrix species in diverse heterotrophic consortia. Kinetic experiments on different initial pollutant concentrations were carried out to determine the ability of the established culture to remove organic load (expressed by d-COD, dissolved-Chemical Oxygen Demand), N and P from agroindustrial wastewaters (dairy, winery and raisin). Biomass and oil productivity were determined. It was found that significant removal rates of nutrients were achieved in all the wastewaters examined, especially in that originated from winery in which the highest d-COD removal rate (up to 97.4%) was observed. The attached microbial biomass produced in winery wastewater contained 23.2% lipid/biomass, wt/wt, which was satisfying. The growth in the dairy wastewater yielded the highest attached biomass productivity (5.03 g m&minus, 2 day&minus, 1) followed by the mixed effluent of winery-raisin (4.12 g m&minus, 1) and the winery wastewater (3.08 g m&minus, 1). The produced microbial lipids contained high percentages of saturated and mono-unsaturated fatty acids (over 89% in total lipids) in all substrates examined. We conclude that the proposed attached growth photobioreactor system can be considered an effective wastewater treatment system that simultaneously produces microbial lipids suitable as biodiesel feedstock.

Several approaches of hydrogenotrophic denitrification of potable water as well as technical data and mathematical models that were developed for the process are reviewed. Most of the applications that were tested for hydrogenotrophic process achieved great efficiency, high denitrification rates, and operational simplicity. Moreover, this paper reviews the variety of reactor configurations that have been used for hydrogen gas generation and efficient hydrogen delivery. Microbial communities and species that participate in the denitrification process are also reported. The variation of nitrate concentration, pH, temperature, alkalinity, carbon and microbial acclimation was found to affect the denitrification rates. The main results regarding research progress on hydrogenotrophic denitrification are evaluated. Finally, the commonly used models and simulation approaches are discussed.

Hexavalent chromium (Cr(VI)) was co-treated either with second cheese whey (SCW) or winery effluents (WE) using pilot-scale biological trickling filters in series under different operating conditions. Two pilot-scale filters in series using plastic support media were used in each case. The first filter (i.e., Cr-SCW-filter or Cr-WE-filter) aimed at Cr(VI) reduction and the partial removal of dissolved chemical oxygen demand (d-COD) from SCW or WE and was inoculated with indigenous microorganisms originating from industrial sludge. The second filter in series (i.e., SCW-filter or WE-filter) aimed at further d-COD removal and was inoculated with indigenous microorganisms that were isolated from SCW or WE. Various Cr(VI) (5–100 mg L−1) and SCW or WE (d-COD, 1000–25,000 mg L−1) feed concentrations were tested. Based on the experimental results, the sequencing batch reactor operating mode with recirculation of 0.5 L min−1 proved very efficient since it led to complete Cr(VI) reduction in the first filter in series and achieved high Cr(VI) reduction rates (up to 36 and 43 mg L−1 d−1, for SCW and WW, respectively). Percentage d-COD removal for SCW and WE in the first filter was rather low, ranging from 14 to 42.5% and from 4 to 29% in the Cr-SCW-filter and Cr-WE-filter, respectively. However, the addition of the second filter in series enhanced total d-COD removal to above 97% and 90.5% for SCW and WE, respectively. The above results indicate that agro-industrial wastewater could be used as a carbon source for Cr(VI) reduction, while the use of two trickling filters in series could effectively treat both industrial and agro-industrial wastewaters with very low installation and operational costs.

A cluster of bench-scale packed-bed reactors was used to investigate nitrate removal from contaminated drinking water through hydrogenotrophic denitrification. A mixed culture originating from a wastewater treatment plant was used to inoculate four packed-bed reactors, with gravel as support media in different sizes (mean diameter 1.75, 2.41, 3.52 and 4.03 mm). We studied the effect of gravel size and operating mode (draw-fill or continuous) on filter performance. It was found that gravel size drastically affects the hydrogenotrophic denitrification rate, while draw-fill operation was more efficient for high nitrate nitrogen concentrations up to 200 mg/L. An increase of filter height increased drastically the retention time of the treated water and continuous operation became favourable for even higher nitrate nitrogen concentrations of 350 mg/L, where denitrification rates of about 6.5 g/Ld were achieved. The proposed procedure may prove to be an effective and economic method for nitrate removal from contaminated water resources.

In this work, competition for two nitrogen resources (nitrate-, nitrite-nitrogen) between three hydrogen oxidizing denitrifying populations (Acidovorax sp. strain Ic3 (X1), Paracoccus sp. strain Ic1 (X2), and Acinetobacter sp. strain Ic2 (X3)) was examined. The dynamics of three systems of microbial populations (system I: X1 − X3, system II: X2 − X3, and system III: X1 − X2 − X3), grown in a chemostat, was studied using bifurcation analysis. The chemostat is the most common type of biological reactor used for the study of microbial growth under controlled conditions. The effect of the operating parameters (i.e., dilution rate and feed nitrate nitrogen concentration) on the long-term behavior of the systems showed that X3 was the predominant population for a wide range of combinations of dilution rate and feed nitrate nitrogen concentration. Also, coexistence of two populations (X2X3, X1X3) was observed. The results of the bifurcation analysis were also used to determine the denitrification rate and the nitrite nitrogen accumulation for each of the three systems as a function of the dilution rate (up to 0.17 h−1) and the feed nitrate nitrogen concentration (up to 300 mg/L). The highest denitrification rate was achieved by system I (28 mg/Lh). A comparison between the three systems showed that the nitrite nitrogen concentration in system I was less than the one in system III, while the two systems gave similar denitrification rates. The second system had the greatest accumulation of nitrites with the lowest denitrification rate.

The dynamics of a model of a free-living nitrogen-fixing population, grown in a chemostat together with a non-nitrogen-fixing bacterial population in competition for the available nutrients and a predator, was studied through bifurcation analysis. When the nitrogen-fixing population is slightly inhibited by ammonium nitrogen (NH 3 ), then this population survives at steady state at low NH 3 concentration for a wide range of dilution rate values. At high NH 3 concentration the nitrogen-fixing population survives at high dilution rate values, while at lower dilution rate values survival of the nitrogen-fixing population is possible when both the competitive population and the predator are present. When inhibition of NH 3 is high, the nitrogen-fixing population survives at steady state at low NH 3 concentrations for a wide range of dilution rate values, while at high NH 3 concentration the competitive prey stimulates the coexistence state of all populations. Therefore, under high NH 3 concentration conditions the competitive population appears to be beneficial for the system and for the survival of the nitrogen-fixing prey. However, the presence of the competitive prey, in the regions where the nitrogen-fixing prey coexists with its predator at a stable state seems to have a negative effect on the nitrogen-fixing activity.

The progress of biological phenol and nitrate removal in batch assays of mixed bacteria culture was examined. The aim was to study the performance of the culture for biological phenol and nitrate removal in synthetic wastewater containing phenol and nitrates at various concentrations, under aerobic conditions. The maximum removal rates achieved were 1.07 mg NO3−-N l−1 h−1 and 27.8 mg phenol l−1 h−1, for feed concentrations 20 mg NO3−-N l−1 and 600 mg phenol l−1 in a draw-fill experiment. The kinetics of the process was studied in batch cultures of suspended bacteria acclimatized in phenol and originated from olive pulp. The rates of phenol and nitrate biological removal were found to be inhibited beyond 40 mg NO3−-N l−1 and 300 mg phenol l−1, respectively. A kinetic model was developed and its kinetic parameters were determined. The growth kinetics could be very well described by using expressions for triple nutrient limitation (nitrate, nitrite, phenol) with inhibition from nitrate and phenol. The proposed model is capable of describing accurately enough, cellular growth, nitrate, nitrite and phenol utilization, in the presence of various concentrations of nitrate (20–100 mg NO3−-N l−1) and phenol (300–950 mg phenol l−1).