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This study evaluates the effectiveness of a pilot-scale high-rate algae-bacteria pond (HRAP) to remove pharmaceutical compounds (PhACs) from municipal centrate. The studied PhACs belonged to different classes of synthetic active compounds: antihypertensives, antiepileptics, antidepressants, neuroprotectors, and anti-inflammatory drugs. The HRAP, growing a mixed microalgal consortium made of Chlorella spp. and Scenedesmus spp., was operated in continuous mode (6 days hydraulic retention time) from May to November 2021. Removal efficiencies were high (>85 %) for Sulfamethoxazole and Lamotrigine, promising (65–70 %) for Metoprolol, Fluoxetine, and Diclofenac but low (30–40 %) for Amisulpride, Ofloxacin, Carbamazepine, and Clarithromycin. Propyphenazone and Irbesartan were not removed, and their concentrations increased after the treatment. The combination of abiotic and biotic drivers (mostly global radiation and the synergy between microalgae and bacteria metabolisms) fostered photo and biodegradation processes. Overall, results suggest that microalgae-based systems can be a valuable solution to remove PhACs from wastewater.

The aim of this study was to acclimate anaerobic prokaryotes to saline microalgae biomass. Semi-continuous experiments were conducted using two 1.5 L mesophilic reactors for 10 weeks, (hydraulic retention time of 21 days). The first reactor was solely fed with sewage sludge (control), while the second received a mixture of sewage sludge and microalgal biomass (80/20 %w/w) cultivated at 70 g·L-1 salinity. The in-reactor salinity reached after the acclimation phase was 14 g·L-1. Biomethane production was comparable between the control and acclimated reactors (205 ± 29 NmLMethane·gVolatileSolids-1). Salinity tolerance assessment of methanogenic archaea revealed that salinity causing 50% inhibition of methane production increased from 10 to 27 g·L-1 after acclimation. Microbial diversity analyses revealed notable changes in methanogenic archaea populations during co-digestion of saline microalgae biomass, particularly methylotrophic (+27%) and acetotrophic (-26%) methanogens. This study has highlighted the possibility of treating efficiently saline microalgae in co-digestion with sewage sludge in future industrial biogas plants.

Large amounts of produced water are extracted by the Oil and Gas energy sector since the industrial revolution. This available water, often salty, can be used to dilute liquid digestate from the anaerobic digestion process, a promising source of nutrients for microalgae cultivation. The study investigates the growth of halotolerant microalgae and their associated bacteria in column photobioreactors (PBRs) and open raceway pond (RWP), to treat industrial wastewaters while producing biomass for energy valorisation. Microalgae were cultured in mixtures of saline artificial produced water (7–44 %v/v), liquid digestate (5 %v/v using PBRs, 29–63 %v/v using RWP) and seawater. Nannochloropsis oceanica and Tetraselmis suecica strains were firstly cultivated in 70 L PBRs in indoor conditions for 3 months and later in 1.1 m3 RWP operated in outdoor conditions for 5 months in spring-summer period. In PBRs, average productivity was 9.0 ± 4.2 gVSS·m−2·d−1 (102–153 mgVSS·L−1·d−1), with daily removal efficiencies for chemical oxygen demand, nitrogen and phosphorous up to 61.8, 31.6 and 97.2 %, respectively. In RWP, strong changes in the microalgae populations were observed. Productivity was 6.7 ± 5.2 gVSS·m−2·d−1 (30 ± 23 mgVSS·L−1·d−1), with daily removal efficiencies for chemical oxygen demand, nitrogen and phosphorous up to 48.4, 44.4 and 88.1 %, respectively. In parallel with the production of microalgae, a nitrifying microbial population grew in the RWP despite the high salinity (70 g L−1). Over these periods of several months, microalgae production was maintained using a culture medium containing high salt concentration, metals and harmful aromatic compounds.

Hydrothermal carbonization (HTC) emerged as an effective technology for the treatment of various types of wet biomass and organic residues, including sewage sludge, offering the potential for sludge reduction and resource recovery. HTC pretreatment impact on downstream sludge fermentation is investigated. Results obtained at optimal conditions for HTC pretreatment (170 °C for 30 min) indicated that soluble carbon was significantly increased in the liquid fraction, enhancing feedstock availability for fermentation. Semi-continuous fermentation of HTC-treated sludge resulted in a stable process in which a mixed microbial community produced volatile fatty acids (VFAs) with longer chain acids content, acidification yield of 0.59 ± 0.05 g COD-VFA g−1 CODin and volumetric productivity of 1.6 ± 0.5 g COD-VFA L−1 d−1. Biomethane Potential tests evidenced high values for hydrochar. Overall, the HTC pretreatment enables improved conversion efficiencies, in the view of valorizing the liquid for VFA synthesis and the hydrochar for biomethane production.

The study explores the use of microalgal-based carbon-encapsulated iron nanoparticles to enhance the anaerobic digestion process. These nanoparticles are synthesized through hydrothermal carbonization (225°C, 3h) by combining iron nitrate with algal biomass grown on urban wastewater (Mantovani et al., 2022; Peng et al., 2014). The nanoparticles have been characterized through ICP-OES, TEM, SEM-EDX, and XRD to understand their morphology, properties, presence and abundance of oxides, and crystalline phases. They were integrated into semi-continuous lab-scale reactors fed with municipal sludges, where different concentrations of nanoparticles (100 mg/L and 500 mg/L) were tested. The results indicated that nanoparticles at 100 mg/L significantly increase methane production by 24% to 180 ± 50 NmL/gVS and biogas production by 30% to 248 ± 58 NmL/gVS compared to the control. Additionally, the presence of nanoparticles improved organic matter degradation and volatile fatty acid conversion. These findings suggest that microalgal-based iron nanoparticles enhance microbial metabolic efficiency, leading to improved biogas yields and a reduction in undesired compounds such as hydrogen sulfide by 54%. It is hypothesized that the inclusion of iron nanoparticles will improve microbial metabolism efficiency, leading to increased methane production while concurrently reducing undesired compounds such as hydrogen sulfide, which will be eliminated via precipitation (Feng et al., 2014).

The integration of microalgae cultivation in anaerobic digestion (AD) plants can take advantage of relevant nutrients (ammonium and ortho-phosphate) and CO2 loads. The proposed scheme of microalgae integration in existing biogas plants aims at producing approximately 250 ty(-1) of microalgal biomass, targeting the biostimulants market that is currently under rapid expansion. A full-scale biorefinery was designed to treat 50 kty(-1) of raw liquid digestate from AD and 0.45 kty(-1) of CO2 from biogas upgrading, and 0.40 kty(-1) of sugar-rich solid by-products from a local confectionery industry. An innovative three-stage cultivation process was designed, modelled, and verified, including: i) microalgae inoculation in tubular PBRs to select the desired algal strains, ii) microalgae cultivation in raceway ponds under greenhouses, and iii) heterotrophic microalgae cultivation in fermenters. A detailed economic assessment of the proposed biorefinery allowed to compute a biomass production cost of 2.8 +/- 0.3 kg DW-1, that is compatible with current downstream process costs to produce biostimulants, suggesting that the proposed nutrient recovery route is feasible from the technical and economic perspective. Based on the case study analysis, a discussion of process, bioproducts and policy barriers that currently hinder the development of microalgae-based biorefineries is presented.

The results of a first campaign of sampling and analyses of emerging micropollutants in the influent (municipal centrate) and effluent of a pilot MBP raceway are reported. The algal population was chiefly made of Chlorella spp. and the pilot worked satisfactorily for the removal of nitrogen. 14 emerging micropollutants were analysed. Average removal efficiencies exceeding 80 % were observed for diclofenac, lamotrigine, ketoprofene, clarithromycin. For such compounds the variability of removal efficiency was also reduced, with respect to the other tested molecules, and was particularly low for diclofenac and lamotrigine. Removal efficiencies over 50 % were measured for azithromycin, metoprolol and irbesartan but with strong variability. Lower removal efficiencies were observed for amisulpride and 5-methylbenzotriazole, while for the remaining compounds the concentrations in the effluent were higher than in the influent.

The efficiency of an outdoor pilot-scale raceway pond treating the wastewaters generated by a large-scale piggery farm in Northern Italy was evaluated. The biomass productivity over 208 days of experimentation was 10.7 ± 6.5 g TSS·m−2·d−1, and ammoniacal nitrogen, orthophosphate, and COD average removal efficiencies were 90%, 90%, and 59%, respectively. Results were used to perform a comprehensive techno-economic analysis for integrating algae-based processes in farms of different sizes (100–10000 pigs). The amount of N disposed of on agricultural land could be reduced from 91% to 21%, increasing the fraction returned to the atmosphere from 2.4% to 63%, and the fraction in the biomass from 6.2% to 16%. For intensive farming, the release of 110 t N·ha−1·y−1 contained in the digestate could be avoided by including algae-bacteria processes. The biomass production cost was as low as 1.9 €·kg−1, while the cost for nitrogen removal was 4.3 €·kg N−1.

Research data produced within the CARIPLO IMAP and Perform Water 2030 projects were processed using the SimaPro software to carry out the Life Cycle Assessment according to ISO 14040-44 of an innovative process of treated effluents' polishing. The study aims to evaluate the integration of a microalgae culture as a side-stream process into the baseline layout of a wastewater treatment plant to remove nitrogen from the supernatant of sludge centrifugation from an environmental perspective. In particular, the investigated system focuses on using the algal biomass produced as an organic matrix for encapsulating zero-valent iron nanoparticles to be used for the final refinement of the effluent. Zero-valent iron (ZVI) is a reactive metal and an effective reducing agent. It can be used to remove organic and inorganic pollutants (e.g., chlorinated organics, pharmaceuticals, metals, textile dyestuffs). The encapsulation of ZVI by hydrothermal carbonization (HTC) in a carbonaceous matrix allows for overcoming the problems related to its lack of stability, easy aggregation, and difficulty in separating the ZVI nanoparticles from the treated solution. The case study refers to Bresso wastewater treatment plant (Milan province, Northern Italy). The environmental performances of the study were assessed following the Life Cycle Impact Assessment methods IMPACT 2002+. According to the results, the new process integration does not affect the environmental performance of the WWTP, still implying a significant improvement in the removal of metals and micropollutants. In fact, due to the ability of ZVI nanoparticles to remove organic and inorganic pollutants, the outflowing load will be significantly reduced, which will improve the environmental performance of the entire Bresso wastewater treatment plant.

This study aims at evaluating an innovative biotechnological process for the concomitant bioremediation and valorization of wastewater from textile digital printing technology based on a microalgae/bacteria consortium. Nutrient and colour removal were assessed in lab-scale batch and continuous experiments and the produced algae/bacteria biomass was characterized for pigment content and biomethane potential. Microbial community analysis provided insight of the complex community structure responsible for the bioremediation action. Specifically, a community dominated by Scenedesmus spp. and xenobiotic and dye degrading bacteria was naturally selected in continuous photobioreactors. Data confirm the ability of the microalgae/bacteria consortium to grow in textile wastewater while reducing the nutrient content and colour. Improvement strategies were eventually identified to foster biomass growth and process performances. The experimental findings pose the basis of the integration of a microalgal-based process into the textile sector in a circular economy perspective.

This study aims at evaluating the process efficiency of an outdoor pilot-scale microalgae-based wastewater treatment system. Experimental results from two monitoring campaigns were analysed, showing that the system removed on average 85.1 % and 36.2 % of the influent ammoniacal nitrogen and orthophosphate, respectively, with an associated algal productivity of 9.5 g TSS·m−2·d-1. Based on pilot-scale results, a comprehensive techno-economic assessment was performed, allowing to calculate a biomass production cost of 4.3 €·kg TSS-1 and a wastewater treatment cost of 2.7 €·m−3 (corresponding to a nitrogen removal cost of 12.5 €·kg N−1). These costs turned out to be comparable with conventional wastewater treatment processes, thus recognizing the potential of microalgae cultivation on wastewaters as feasible alternative to conventional energy-demanding bioremediation systems and to expensive algal cultivation processes. A sensitivity and scenario analysis indicated that, under the most optimistic condition (20 % increase in the productivity, and 20 % OPEX and CAPEX reduction), biomass production and nitrogen removal costs could be further reduced of approximately 44 %.

Metal-based flocculants are commonly used for biomass harvesting in microalgae-based bio-refineries. Besides the high separation efficiency, additional aspects should be considered, related to the toxicity of metals for the algal biomass. Partitioning tests for commonly used flocculants (i.e., FeCl3 and Al2(SO4)3) showed that metals were mostly transferred to the solid phase with more than 95% of dosed metal ending up into the biomass, and low metal concentrations in the liquid effluent (lower than 0.4 mg L−1 for both metals), thus allowing for water reuse. Photosynthesis inhibition was tested on microalgae and microalgae-bacteria cultures, using a standardized photo-respirometry protocol in which typical concentrations used during coagulation-flocculation were assessed. Modelling dose-response curves, concentrations corresponding to 50% inhibition (IC50) were obtained, describing short-term effects. The obtained IC50 ranged from 13.7 to 28.3 mg Al L−1 for Al, and from 127.9 to 195.8 mg Fe L−1 for Fe, showing a higher toxicity for the Al-based flocculant. The recovery of photosynthesis inhibition was also quantified, to evaluate the possibility of reusing/recycling the harvested biomass. The results highlighted that the residual photosynthetic activities, evaluated after 1 h and 24 h of exposure to metals were partially recovered, especially for Al, passing from 67.3% to 94.6% activity, respectively, while long-term Fe effects were stronger (passing from 64.9% to 77.6% activity). A non-toxic flocculant (cationic starch) was finally tested, excluding potential effects due to biomass aggregation, as the reduction of photosynthetic activity only reached 3.4%, compared to control. Relevant modifications to the light availability and the optical properties of algal suspensions were assessed, identifying a strong effect of iron which caused an increase of the light absorbance up to approximately 40% at high Fe concentrations. Possible implications of dosing metallic flocc

The treatability of seven wastewater samples generated by a textile digital printing industry was evaluated by employing 1) anammox-based processes for nitrogen removal 2) microalgae (Chlorella vulgaris) for nutrient uptake and biomass production 3) white-rot fungi (Pleurotus ostreatus and Phanerochaete chrysosporium) for decolorization and laccase activity. The biodegradative potential of each type of organism was determined in batch tests and correlated with the main characteristics of the textile wastewaters through statistical analyses. The maximum specific anammox activity ranged between 0.1 and 0.2 g N g VSS-1 d-1 depending on the sample of wastewater; the photosynthetic efficiency of the microalgae decreased up to 50% during the first 24 hours of contact with the textile wastewaters, but it improved from then on; Pleurotus ostreatus synthetized laccases and removed between 20-62% of the colour after 14 days, while the enzymatic activity of Phanerochaete chrysosporium was inhibited. Overall, the findings suggest that all microbes have great potential for the treatment and valorisation of textile wastewater after tailored adaptation phases. Yet, the depurative efficiency can be probably enhanced by combining the different processes in sequence.

This study investigates the environmental improvements associated to the integration of a microalgae unit as a side-stream process within an existing municipal wastewater treatment facility in northern Italy. Microalgae are fed on the centrate from sludge dewatering, rich in nutrients, and on the CO2 in the flue-gas of the combined heat and power unit. The produced biomass is recirculated upflow the water line where it settles and undergoes anaerobic digestion generating extra biogas. A life cycle assessment was performed collecting primary data from an algal pilot-scale plant installed at the facility. Fifteen environmental indicators were evaluated. Compared to the baseline wastewater treatment, the new algal configuration allows an improvement for 7 out of 15 indicators mainly thanks to the electricity savings in the facility. Some recommendations are provided to improve the performance of the algal system in the scaling up.

This study aimed at evaluating the effects of different environmental conditions (irradiance, temperature, pH and dissolved oxygen) on a microalgae-bacteria consortium cultivated in a pilot-scale open pond and fed on the liquid fraction of anaerobic digestate. A standardized photo-respirometry protocol was followed to evaluate the activity of microalgae under different conditions. Two datasets (specific photosynthetic oxygen production rates and respiratory oxygen consumption rates) were obtained for each environmental parameter, throughout the entire range of conditions found in the outdoor cultivation system. Different kinetic models available in literature were fitted to experimental data and the resulting outputs were compared through model selection estimators, in order to select the most appropriate equations. The proposed set of equations constitute a modelling tool for the prediction of algal growth rates in algae-bacteria systems, as a function of environmental conditions.

The role of P content on the treatment and valorization of the liquid fraction of digestate, namely centrate, through microalgae-based technologies was evaluated in this study. The performance of four column photobioreactors, which were fed on diluted centrate with corrected (10 mg N/ mg P) and not modified (129 mg N/ mg P) N:P ratio, were monitored and compared. The results demonstrated that P shortage in the centrate affected neither the total nitrogen and COD removal rate nor the volumetric biomass productivity, suggesting that expensive addition of P salts is not necessary to maximize the efficiency of the process. On the contrary, the addition of P to the centrate promoted the ammonia oxidation process as higher nitrite production was observed in the photobioreactors with adjusted N:P ratio than in the ones fed with the non-adjusted N:P ratio. These findings were confirmed by fluorescence in-situ hybridization and quantitative PCR assays, which revealed a higher number of ammonia-oxidizing bacteria in the microalgal suspensions cultivated on centrate with P addition. In conclusion, the N:P ratio in the centrate seems to have a role in controlling the nitrification process rather than in the overall nutrient removal rate and biomass productivity of the microalgae-based system.

The use of phototrophic organisms in wastewater treatment is gaining increasing interest, due to the possibility of exploiting photosynthetic oxygenation, thus lowering treatment costs and environmental impacts. Mixed consortia of phototrophic organisms and aerobic bacteria rapidly develop in photobioreactors receiving wastewaters; in this case, the complex mutualistic interactions among microorganisms cannot be easily described, making difficult to forecast removal efficiencies and biomass productivities. Respirometric methods are applied for evaluating bacterial activity in activated sludge (conventional respirometry) or photosynthetic activity in phototrophic organisms (photorespirometry). Photo-respirometric methods can be also exploited for monitoring algae-bacteria systems and for calibrating mathematical models, allowing for a better comprehension of the interactions involved and a more accurate prediction of system efficiencies. A general protocol and a series of guidelines for conducting photorespirometric tests on algal-bacterial suspensions are here proposed, based on the review of experimental protocols applied to evaluate the effects of several parameters on these systems.

Milk whey processing wastewaters (MWPWs) are characterized by high COD and organic nitrogen content; the concentrations of phosphorus are also relevant. A microalgal-based process was tested at lab scale in order to assess the feasibility of treating MWPW without any dilution or pre-treatment. Different microalgal strains and populations were tested. Based on the obtained results, Scenedesmus acuminatus (SA) and a mixed population (PM) chiefly made of Chlorella, Scenedesmus, and Chlamydomonas spp. were grown in duplicate for 70 days in Plexiglas column photobioreactors (PBRs), fed continuously (2.5 L culture volume, 7 days hydraulic retention time). Nutrient removal, microalgae growth, photosynthetic efficiency, and the composition of microalgal populations in the columns were monitored. At steady state, the microalgal growth was similar for SA and PM. The average removal efficiencies for the main pollutants were: 93% (SA), 94% (PM) for COD; 88% (SA) and 90% (PM) for total N; and 69% (SA) and 73% (PM) for total P. The residual pollution levels in the effluent from the PBRs were low enough to allow their discharge into surface waters; such good results were achieved thanks to the synergy between the microalgae and bacteria in the CO2 and oxygen production/consumption and in the nitrogen mineralization.

Tetraselmis suecica was cultivated in a semi-continuously operated tubular photobioreactor fed on aquaculture wastewater (AW) testing two hydraulic retention times (HRT): 10 and 7 days (RUN_1 and RUN_2, respectively). The integrated mechanistic model BIO_ALGAE was validated with experimental data in order to simulate the biomass production and nutrient uptake of T. suecica. Moreover, AW was used as substitute synthetic cultivation medium to test the production of lipids, proteins, and carbohydrates in the microalgal biomass. Preliminary photo-respirometric tests were carried out on the AW suspension containing microalgae and bacteria. Dissolved Inorganic Nitrogen (DIN) and Dissolved Inorganic Phosphorus (DIP) were analyzed for the two RUNs, and no significant difference was highlighted (p > 0.05). On the contrary, the productivity of the Total suspended solids (TSS) was significantly higher (p < 0.05) for RUN_1 (900 mg TSS/L) than for RUN_2 (550 mg TSS/L). The analysis of the biochemical composition of biomass has demonstrated a higher content of proteins than of lipids and carbohydrates for the two RUNs. BIO_ALGAE model was validated by comparing simulated results to experimental data. The model was able to reproduce the pattern of these experimental data quite well, for both nutrient uptake and biomass production. The simulated curve follows the same pattern as the experimental data for both RUNs. The wavelike trend indicates the good accuracy of the simulated curves to reproduce the microalgae growth and nutrient uptake that occurring during daytime and at night. With this study, BIO_ALGAE Model was demonstrated to be useful to simulate bioremediation and microalgae production in aquaculture wastewater in a semi-continuous system with different environmental factors. The photo-respirometric outputs were compared with the process rates affecting dissolved oxygen dynamics computed by the mathematical model.

This study aims at demonstrating the feasibility of using microalgae-bacteria consortia for the treatment of the sidestream flow of the supernatant from blackwater dewatering (centrate) in an urban wastewater treatment plant in Northern Italy. A 1200 L raceway reactor was used for the outdoor cultivation of a diverse community of Chlorella spp., Scenedesmus spp. and Chlamydomonas spp. in continuous operation mode with 10 days hydraulic retention time. During the trial, an average daily areal productivity of 5.5 ± 7.4 g TSS m−2 day−1 was achieved while average nutrient removal efficiencies were 86% ± 7% and 71% ± 10% for NH4-N and PO4-P, respectively. The microalgal nitrogen assimilation accounted for 10% of the nitrogen in the centrate while 34% was oxidized to nitrite and nitrate. The oxygen produced by microalgae fully covert the oxygen demand for nitrification. This suggests that the proposed process would reduce the aeration demand for nitrification in the water line of the plant, while producing algal biomass to be further valorized for energy or material recovery.

BACKGROUND: Secondary effluent wastewaters still contain resources including water and nutrients that must be safely reused and recovered. In this study, the combined role of microalgae as disinfectant and nutrient removal agent was evaluated for the potential application of a microalgae-based process as a cost-effective tertiary treatment. Nutrient removal, biomass productivity and disinfection performances were monitored in laboratory-scale photobioreactors (batch and continuous) fed on a secondary effluent mixed with a 10% on influent collected at a large municipal wastewater treatment plant where tertiary disinfection is performed by UV treatment. RESULTS: In microalgae-based batch disinfection tests, Escherichia coli counts (0.5 ± 0.7 log CFU 100 mL−1) were comparable to those after traditional UV process (0.7 ± 0.84 log CFU 100 mL−1) and lower than in tests where light was applied without microalgae. In the following continuous test, E. coli counts were reduced by one order of magnitude and the pathogenic strain of E. coli O157:H7/H−, Salmonella spp. and indicators such as Bacteroides spp. and Enterococcus spp. were never detectable in the effluents by molecular tools. Total nitrogen and phosphorus removals reached 93 and 100%, respectively, while the algal biomass productivity of the system averaged 50 ± 30 mg TSS L−1 day−1. CONCLUSIONS: The effluents of the photobioreactors reached quality standards appropriate for water reuse. Moreover, nutrients could be recovered through the generation of algal biomass suitable for further valorization. © 2019 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

BACKGROUND: Microalgae–bacteria-based processes are among the most promising low-cost technologies to treat livestock wastewaters. The current literature reports the need for pretreatment or dilution of piggery wastewater for adequate microalgal growth. The aim of this study is to optimize the potential of microalgal–bacterial communities to treat undiluted and untreated piggery wastewater by investigating the influence of some operational parameters such as phosphorus and CO 2 availability and hydraulic retention time on the nitrogen removal efficiency and biomass productivity. RESULTS: The microalgal community (dominated by Chlorella spp.) developed quickly and remained quite stable. The rates of biomass production and NH 4 -N removal were 55 ± 30 mg TSS L −1 day −1 and 13 ± 3 mg NH 4 -N L −1 day −1 respectively. CO 2 adjustment had a positive effect on microalgal growth and NH 4 -N removal. CONCLUSION: Data confirm the ability of the microalgal–bacterial consortium to grow on undiluted and untreated piggery wastewater under semi-continuous conditions. Synergy between algae and bacteria seems positive since photosynthesis produces the oxygen needed for ammonia oxidation