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Activated sludge process is the common industrial wastewater treatment scheme. However, intensive aeration requirements made it impossible for wastewater treatment plants (WWTPs) to be energy- positive. The current study designed energy positive industrial wastewater treatment trains by using innovative technologies such as micro-sieving, up-flow anaerobic sludge blanket (UASB), and partial nitrification/Anammox (PN/A). Excel-based models were developed to compare the innovative treatment systems and the activated sludge system based on unit energy, cost and environmental indicators. Results showed that the innovative systems could save unit energy and cost by 67–85% and 59–85%, respectively. Innovative technologies increase the average unit energy production for meat processing, tannery, and textile wastewater treatment up to 1.71, 1.63, and 1.58 kWh/kg BODremoved. Furthermore, the high energy recovery reduces the overall global warming potential of these systems. Electrical self-sufficiency in industrial wastewater treatment could be obtained by using innovative technologies, which present great potential for future designs of industrial wastewater treatment.

Electrochemical processes have proven their potential as effective technologies to treat wastewater from industrial, urban and agricultural activities, and thus, contribute towards a cleaner environment. In this study, we aimed to assess the effectiveness of the leading electrochemical technologies, such as electro-oxidation, electrochemical coagulation and electrochemical advanced oxidation processes (EAOPs), statistically for different types of anodes for the removal of various pollutants from wastewater along with their treatment efficiency. Anode is considered as a source of electron and an essential part of electrochemical processes. So, we have evaluated the relationship between different anode features such as anodic material, surface area versus removal of chemical oxygen demand (COD), dissolved organic carbon (DOC) and colour in various wastewater treatment plants (WWTPs) by IBM SPSS Statistics 26. Apart from that, various process characteristics such as inter-electrode distance, system pH, reactor volume, current density and voltage were also considered in this investigation. From the regression analysis of the electrochemical coagulation system, it was found that the removal efficiency of pollutants is enhanced by the surface area of the electrodes along with the inter-electrode distance. Regarding electro-oxidation, it was seen that COD and colour removal are both dependent on the reaction time of the system, while the DOC removal rate of different EAOPs was strongly related to the reactor volume. Furthermore, the uncertainty of the regression analysis on pollutant removal efficiency prediction was assessed. Finally, sensitivity analysis was done by Monte-Carlo method to check modest changes from input variables.

Anaerobic co-digestion of lignocellulosic biomass and food waste (FW) has been extensively applied. However, whether hydrothermal pretreatment (HTP) of lignocellulosic biomass can enhance the performance in co-digestion deserves further investigation. In this study, corn cob (CC) was adopted as a typical lignocellulosic biomass for co-digestion with FW at different VS ratios of 1:3 (S1–S4) and 1:6 (S5–S8), attempting to evaluate the effect of HTP of CC at different temperature gradients (125, 150 and 175 °C) on the co-digestion performance. The emphasis was placed on hydrolysis, acidification and methanogenesis for different feedstock conditions. Results illustrated that the HTP had a certain destroying effect on the lignocellulose structure in CC and the crystallinity of cellulose decreased, significantly facilitating its co-digestion with FW. For FW/CC co-digestion at the VS ratio of 1:3, the S3 group (CC was pretreated at 150 °C) reached the maximum cumulative biogas yield (CBY) of 4660 mL and the maximum specific methane yield (SMY) of 316.9 mL/g·VS. Moreover, at 1:6, S7 group (pretreated at 150 °C) exhibited the optimal CBY of 4100 mL while achieving the SMY of 277.6 mL/g·VS among the digesters, indicating that the co-digestion of pretreated CC and FW could achieve higher methane production, and 150 °C refers to the optimal pretreatment temperature. Moreover, the peak values of the accumulated VFAs in digesters S1–S4 (2000–3000 mg/L) is higher than that in digesters S5–S8 (800–1500 mg/L). As suggested from microbial community and diversity date, the HTP expedited the enrichment of system hydrolyzing and acidogenic bacteria. These results are significant and provide certain guidance for optimizing the co-digestion of FW and CC in actual engineering.

The intensification of milk production in Brazil in the past decade has imposed great stress on the environment. Therefore, it is very important to find a balance between economic, social, and environmental objectives. The paper assesses the economic costs by production systems: confined feedlot, semi-confined feedlot, and pasture in the south of the country. The economic assessment was realized on some investment analysis tools and the GHG emissions costs for the different production systems indicated. Our results show that hectare and the total area of rural properties were lower in the confined feedlot system, followed by the semi-confined feedlot system and pasture-based grazing system. However, the reduction of the need for feed inputs in the pasture system resulted in lower feeding costs when compared to the other systems. The hectare analysis suggested that the superior productivity of the semi-confined system conditioned higher emission costs in relation to the other systems. However, considered the total emissions of the systems, the pasture system obtained higher values, justified by the greater need for an area for production. The results showed that the higher the food efficiency of a system, the greater the profitability.

One of the challenging tasks of the century is to clean up the contaminants of the environment by ecofriendly, sustainable and economically adoptable technologies. The application of quantum dots (QDs) is growing rapidly in to the field of nanotechnology. The electronic properties such as the energy of the highest occupied molecular orbital (EHOMO), the lowest unoccupied molecular orbital (ELUMO), the energy gap ΔE are correlated to the size of quantum dots (QDs) such as CdSe in the presence of different ligands. Linear regression equations were developed through statistical analysis using SPSS. In terms of correlation coefficient R2, both the size and nature of organic ligand capping affect the EHOMO, ELUMO and ΔE levels of QDs. Among all QDs, CdSe has the strongest correlation between its frontier molecular orbital energy levels with the QDs size. The R2 value is greater than 0.63 for a regression equation with a coefficient value of −0.17 and a constant of 2.9. This result implies that a unit decrease of size in the range lower than 7 nm would increase the band gap ΔE by 17%. Potential environmental applications of QDs are presented.

Remediation of uranium (U) contamination in the deep vadose zone (VZ) sediments abundant in calcite mineral is a challenging task considering the formation of highly stable and mobile uranyl complexes with carbonate and calcium in pore water composition. There is a concern that uranium contamination in the VZ can serve as a continued source for groundwater pollution, creating a risk to human health and the environment through the groundwater pathway. This requires in-situ remediation of the radionuclide-contaminated VZ to convert soluble U species to low solubility precipitates that are stable in the natural environment. Injection of reactive gasses (e.g., NH3) is a promising technology to decrease U mobility in the unsaturated zone without the addition of liquid amendments. The NH3 injection creates alkaline conditions that can alter the sediment pore water composition due to a release of elements from minerals (via desorption and dissolution) that are present in the sediment. However, it is not known how VZ pore water constituents (Si, Al3+, HCO3−, and Ca2+) would affect U(VI) removal/precipitation in alkaline conditions. This study quantified the role of major pore water constituents typically present in the arid and semi-arid environments of the western regions of the U.S and identified solid uranium-bearing phases that could potentially precipitate from solutions approximating pore water compositions after pH manipulations via ammonia gas injections. Triplicate samples were prepared using six Si (5, 50 100, 150, 200, and 250 mM), six HCO3− (0, 3, 25, 50, 75, and 100 mM), and two Ca2+ (5 and 10 mM) concentrations. The concentration of aluminum and uranium was kept constant at 5 mM and 0.0084 mM, respectively, in all synthetic formulations tested. Results showed that the percentage of U(VI) removal was controlled by the Si/Al molar ratios and Ca2+ concentrations. Regardless of the bicarbonate concentration tested, the percentage of U(VI) removed increased as the Si/Al ratios were increased. However, higher Ca concentrations correlated with higher U(VI) removal, ranging between 96% and 99%, at low Si/Al ratios. The SEM images of dried precipitates displayed dense amorphous regions high in silica content, where EDS elemental analysis unveiled higher U atomic percentages. The formation of uranyl silicate and carbonate minerals was also predicted by the speciation modeling. XRD analysis revealed the presence of uranyl carbonate mineral phases (andersonite, grimselite); however, uranyl silicates predicted (Na-boltwoodite) were not identified experimentally, possibly due to the amorphous nature of the silica solid phases observed in our experiments.

Fenton reaction was used to produce hydroxyl radicals under conditions similar to AOPs with 5,5-dimethyl-1-pyrroline- N -oxide (DMPO) as a spin trap agent in electron paramagnetic resonance (EPR) analysis. A theoretical kinetics model was developed to determine conditions under which the spin-adduct DMPO-OH is not further oxidized by Fe 3+ and excessive radicals, so that hydroxyl radicals concentration could be accurately inferred. Experiments were designed based upon the model and H 2 O 2 and Fe 2+ concentrations were varied from 1 to 100 mM and from 0.1 to 10 mM, respectively, with a constant H 2 O 2 : Fe 2+ ratio of 10:1. Results confirmed that DMPO concentration should be at least 20 times higher than the concentration of H 2 O 2 and 200 times higher than iron concentration to produce stable DMPO-OH EPR signal. When DMPO: H 2 O 2 ratio varied from 1 to 10, DMPO-OH could generate intermediates and be further oxidized leading to the apparition of an additional triplet. This signal was attributed to a paramagnetic dimer: its structure and a formation mechanism were proposed. Finally, the utilization of sodium sulfite and catalase to terminate Fenton reaction was discussed. Catalase appeared to be compatible with DMPO. However, sodium sulfite should be avoided since it reacted with DMPO-OH to form DMPO-SO 3 .

Hydrophobicity, as measured by Log P, is an important molecular property in assessing toxicity and carcinogenicity of disinfection by-products (DBPs). With increasing public health concerns of DPBs, there are considerable benefits in developing Quantitative Structure Activity Relationship (QSAR) models, capable of accurately predicting Log P, which could be used in health risk assessment of DBPs. In this research, Log P values of 46 halogenated alkanes, as one class of DBP compounds, were used to develop QSAR models for this class. Three molecular descriptors, namely, Energy of the Lowest Unoccupied Molecular Orbital (ELUMO), Number of Chlorine (NCl) and Number of Carbon (NC) were used in Multiple Linear Regression (MLR) analysis. The QSAR models developed were validated according to the principles set up by the Organization for Economic Co-operation and Development (OECD). Model Applicability Domain (AD) of the developed QSAR models was defined and mechanisms were interpreted. Considering large number of halogenated alkane compounds, the established QSAR models performed very well in terms of goodness-of-fit, robustness and predictability. The predicted values of Log P of DBPs by the QSAR models have correlation coefficient R2 from 81 % to 98 % with the observed Log P. The leverage approach by Williams plot was applied to detect and remove outliers. As a result, the correlation coefficient, R2, of the QSAR models increased by approximately 2 % to 13 %, before and after removing the outliers, respectively. The developed QSAR model was statistically validated for its predictive power of Log P by the Leave-One-Out (LOO) and Leave-Many-Out (LMO) cross validation methods.

In research, design, and validation of UV disinfection systems of a given bacteria, shoulder effect makes prediction of fluence required difficult. This study theoretically analyzes the fluence required to inactivate any bacteria vs. E. coli as the reference bacteria, at the same Log I. Bacteria sensitivity index (BSI) is defined as the ratio between the inactivation rate constant ki of any bacteria for the linear portion of the dose response curve to that kir of E. coli. Among three sets of fluence requirement reported by the US EPA [4] , Sommer et al. [5] , [20] , and Chang et al. [6] , the fluence required from the EPA is selected as the most suitable reference according to its predictive power as well as regulatory purpose. In the present study, shoulder broadness (SB), H0, is approximated with the intercept of the linear portion at the Log I = 0. A universal equation which can be used to predict the fluence required of any bacteria with a shoulder: H = (0.914 ± 0.055) * (BSI)E * (Log I) + H0. Furthermore, shoulder broadness index (SBI) is defined as the ratio between the fluence difference of any bacteria and the reference bacteria such as E. coli divided by the SB of E. coli. To validate the equation, an independent set of fluence data during UV disinfection of four different ARBs reported by McKinney and Pruden [8] was used. When the predicted fluence by using BSI of the ARBs is compared with the reported fluence at different Log I levels with less than 10% error with Log I up to 5.

Decolorization of Acid Blue 161 (AB161) by solid peroxides such as CaO2 and Na2O2 catalyzed by iron in aqueous solution was investigated. The effect of initial pH, concentration of H2O2, Fe2+, and AB161 on the decolorization kinetics was investigated and compared with the results by liquid H2O2. The experimental results show that decolorization of AB161 follows the second-order kinetic. The second decolorization rate constants and oxidation efficiency at different initial pH, Fe2+, H2O2, and AB161 concentration were correlated with dimensionless ratios such as H2O2/Fe2+ or H2O2/AB161. About two dozens of correlation equations are developed in this paper to quantify the effect of the variables on the decolorization rate constants of AB161. Among solid peroxides such as CaO2 and Na2O2 and liquid H2O2, the optimal pH and [Fe2+] are 2.5 and 5.0 × 10−4 mol L−1, while the concentration of CaO2, Na2O2, and H2O2 is 0.30, 0.25 g L−1 and 3.1 × 10−3 mol L−1, respectively. Our experimental results show that d...

The Fenton process is evaluated as a treatment method to reduce the total organic carbon (TOC) and increase biodegradability of the organic substrate in a mature landfill leachate. Biodegradability was quantified in terms of the ratios between biochemical oxygen demand after 5 days (BOD5) to chemical oxygen demand (COD) (after different Fenton reaction times), and BOD5 (after different Fenton reaction times) to initial BOD5 (original leachate sample), termed as BOD5,0, respectively. An increased TOC removal and improved BOD5/COD ratios were observed following the pH sequence of 3.5 > 6.0 > 2.0. The maximum TOC removal of 61 % and the highest BOD5/COD ratio from 0.11 to 0.37 were observed at pH 3.5. To quantify biodegradability enhancement at different COD loading factors (LCOD) by the Fenton process, the H2O2/Fe2+ ratio was fixed at 1.8 (w/w) and LCOD ranged from 0.22 to 1.19. Experimental results showed that higher TOC removal and biodegradability enhancement were obtained at lower LCOD. Quantitatively, two linear regression equations between LCOD and biodegradability (in terms of BOD5/COD and BOD5/BOD5,0) were established, as: BOD5/COD = 0.57–0.38 LCOD and BOD5/BOD5,0 = 1.40–0.40 LCOD with correlation coefficients (R 2 ) of 0.87 and 0.51, respectively. The experimental work described here, demonstrated that the Fenton process can be used as an effective pre-treatment strategy to increase leachate biodegradability within a short reaction time from 1 to 5 min.

Retrofitting municipal wastewater treatment plants (WWTPs) to energy positive is a major challenge faced by many water utilities. Selection of innovative technologies to achieve retrofitting goals is critical for capital improvement programs in WWTPs. This paper aims to provide a statistical analysis method of unit energy consumption in conventional Finnish WWTPs, presenting Mikkeli WWTP as a case study. The average energy consumption at Finnish WWTPs was quantified as a mean of 0.49 kWh/m3 with a standard deviation of 0.197. The statistical analysis showed that the total energy consumption in Finnish WWTPs are positively correlated with inflow rate and sludge production. However, the unit energy consumption decreases with increasing plant capacity. The energy benchmarking of Mikkeli WWTP confirmed the energy gap of 0.11 kWh/kg COD in electricity. The major energy saving potentials are attributed to secondary treatment, screening and grit removal, and influent pump stations. A plausible innovative retrofitting strategy comprising four emerging energy-neutral or positive technologies is proposed to maximally harness the chemical energy content in wastewater: enhanced primary sedimentation, staged anaerobic fludized membrane bioreactor (SAF-MBR) with completely autotrophic nitrogen removal over nitrite process (CANON), and co-digestion of sludge with organic food-waste. The net energy balance of emerging technologies showed a maximum energy saving potential of 1.26 kWh/kg COD, which could be sufficient to overcome the energy gap of Mikkeli WWTP, providing net positive energy surplus of 1.15 kWh/kg COD.

Chlorinated Alkane (CA) is one of the major classes of Disinfection By-Products (DBPs) in chlorinated drinking water. Multi-multivariate regression methods have been used to develop Quantitative Structure-Activity Relationship (QSAR) models between the Energy of the Lowest Unoccupied Molecular Orbital (ELUMO) and three molecular descriptors: namely, number of chlorine (NCl), number of carbon (NC) and the Energy of the Highest Occupied Molecular Orbital (EHOMO). Among different linear QSAR models, the most robust model is ELUMO=-0.1474NCl-0.003766NC+1.9528EHOMO+1.0664 (N=30, R2=0.956, F=188.498, RMSE=0.00762, P=0.000). The model is validated by using internal and external cross validation techniques. The model uncertainties are also quantified through the Bootstrapping and the Taylor methods. Among all the molecular descriptors, number of chlorine (NCl) contributes to the most to the ELUMO of chlorinated alkanes.

This study assessed anaerobic biodegradability of organic compounds from microorganism activity. Dehydrogenase activity can be a good parameter characterizing the microorganism activity. A modified method of 2-(p-iodophenyl-3-(p-nitrophenyl)-5-pheny tetrazolium chloride-dehydrogenase activity determination was proposed in anaerobic biodegradability assessment. Cubic spline curves were adopted to link the data points. This curve was integrated twice to calculate areas. The microorganism activity index in anaerobic biodegradability assessment was calculated by standardizing the integral. According to the results of the activity index, 14 kinds of organic compounds were classified into readily, partially, and poorly biodegradable under anaerobic conditions, respectively. As a result, some conclusions for anaerobic biodegradability of organic compounds were reached, based on the activity index value.

Oxidation kinetics and mechanisms of four trihalomethanes (THMs) commonly found in chlorinated drinking water by Fenton's reagent were investigated. All the experiments were carried out in air-tight and well-mixed batch reactors in which no headspace was allowed in order to minimize volatilization of any THM during reaction. The optimum dosages of H 2 O 2 and Fe 2+ in the oxidation of bromoform was 3.7-1.9 m m for all the initial concentrations at pH 3.5. The maximum bromoform degradations of 85, 78 and 65% at 3 min were achieved for bromoform concentrations of 295, 98.3 and 49.2 μg/l, respectively. The pseudo-first-order oxidation constants of THMs increase with the increasing number of bromine atoms present in a THM molecule, with bromoform being oxidized the fastest and bromodichloromethane being oxidized the slowest. No oxidative degradation of chloroform was oberved, because the losses in chloroform concentration during the oxidation experiments are the same as what was observed in control experiments. Experiments conducted on the THM mixtures gave similar results in terms of extent of observed oxidative degradation, the amount of THM oxidized increased with increasing initial organic concentrations. The oxidation rate constants for each THM in the mixture also increased as the number of bromine atoms present in a THM molecule increased, with bromoform exhibiting the fastest kinetic rates and bromodichloromethane exhibiting the slowest kinetic rates.

An oxidation kinetic model of trichloroethylene (TCE) by Fenton's reagent is developed based upon transition state theory. Hydroxylated active complexes are assumed to be the transition state after hydroxyl radicals have attacked the organic compound. The complex can either disproportionate into Cl‐ and the other products, or return to their original reactants. Because both hydroxyl radicals and the active complexes have extremely high reactivity, their steady‐state concentrations are assumed constant in developing the kinetic model. The model indicates that Fenton oxidation is first order with respect to the organic concentration. The degree of oxidation is dependent upon the dosage of H2O2 and Fe2+. Because H2O2 and Fe2+ can also react with hydroxyl radicals, neither of them should be overdosed if maximal reaction rate is to be achieved. Experiments have been conducted to obtain rate constants for three different chloroethylenes and chloroethane. It is found that the model is valid only for uns...

The effect of chlorine content of chlorinated phenols on their oxidation kinetics by Fenton's reagent was evaluated through different kinetic studies. First, elementary oxidation rate constants between hydroxyl radicals and 2,4-DCP, 2,4,6-TCP as determined in this study are 7.2∗10 9 M −1 s −1 and 6.3∗10 9 M −1 s −1 respectively.The relative ratios between the rate constants of 2-CP and 2,4,6-TCP referred to the rate constant of 2,4-DCP indicates that the reactivity of chorophenols decreases with increasing substitution of chlorine on the aromatic ring. Second, the pseudo-first order oxidation kinetic constants at overdosed H 2 O 2 and Fe 2+ were proportional to the number of unsubstituted positions, while no correlation between dechlorination constants and the number of unoccupied sites on the aromatic ring was found.Third, dechlorination kinetic model as a function of 11202, Fe, and chlorophenol concentration was developed. At constant 11202 concentration of 5 ∗ 10 −3 M, the observed dechlorination rate constants for 2-MCP, 2,4-DCP, and 2,4,6-TCP are 1.16∗10 7 M −1 s −1 , 2.28∗ 10 7 M −1 s −1 and 4.36∗10 8 M −1 s −1 , respectively. All of these results demonstrated that the oxidation rate constants decrease with increasing content of chlorine. In addition, the initial dechlorination rates do not change significantly for all the chlorinated phenols studied at constant 11202 and Fee* concentration, which suggests that the limiting step in Fenton chemistry is the generation of hydroxyl radicals through H 2 O 2 and Fe 2+ .

The oxidation kinetics and mechanisms of Reactive Red 120, Direct Blue 160, and Acid Blue 40 by H2O2/iron powder system were investigated in a well-mixed batch reactor. Optimal pH ranged from 2.0 to 3.0 depending upon the dye molecular structure and the iron dissolution rate. The optimal ratio of H2O2 to iron metal was 0.001 M to 1.0 g/L. The initial oxidation rates were obtained according to pseudo-first-order kinetics. Dye molecular structure is an important factor that influences decolorization kinetics. The results suggest that the structure chromophore including Azo bonds are the primary target oxidized by H2O2/Fe powder system. The less substituted anthraquinone ring in Acid Blue 40 is more readily to be destroyed than the Azo dyes. Dimerization may take place at high concentration of Acid Blue 40, which decreases the decolorization efficiency. In addition, the color change during decolorization processes may also result from the dye complexes with the iron species. As a result, H2O2/iron powder system is better than the Fenton s reagent system, e.g., H2O2Fe2+, due to the continuous dissolution of iron powder and the dye adsorption on the iron powder, despite the fact that Fenton's reaction was the major process contributing to decolorization.

Photocatalytic oxidation kinetics of five commercial dyes, namely Acid Blue 40, Basic Yellow 15, Direct Blue 87, Direct Blue 160, and Reactive Red 120 was studied in a TiO2/UV slurry reactor. The oxidation kinetics of Direct Blue 160 and Reactive Red 120 follows the Langmuir-Hinshelwood kinetic model at all the pH values studied. However, the oxidation kinetics of Acid Blue 40 fits the model at pH 3, Basic Yellow at pH 3, 5, and 11, and Direct Blue 87 at pH 7 and 9 only. In neutral solution of pH 7, the oxidation rates follow the decreasing order: Direct Blue 87 > Reactive Red 120 > Basic Yellow 15 > Acid Blue 40 > Direct Blue 160. At pH 3, the number of azo linkages in dye molecules seems to be the most important factor. For example, the oxidation rate of monoazo dye of Basic Yellow 15 is faster than disazo dye of Reactive Red 120 which in turn is faster than triazo dye of Direct Blue 160. The fastest reaction rate constants are 0.0160-0.0109 mM/min for monoazo dye of Basic Yellow 15, and the slowest reaction rate constants are 0.0013–0.0021 mM/min for the triazo dye of Direct Blue 160. The effect of Fe2+ and H2O2 on the reaction kinetics was also explored.

Photocatalyzed oxidation kinetics and mechanism of Acid Blue 40 at different pH values by TiO2/UV were studied. It is found that at pH 3, photocatalytic oxidation kinetics of Acid Blue 40 follows the Langmuir-Hinshelwood model, with reaction rate constant k of 0.0074 mM/min and adsorption constant K of 7.05 l/mM; While at higher pH values, no adequate kinetic model can be used. A yellow intermediate has been detected. Its appearance and disappearance with the reaction time are measured in terms of absorbance intensity. More than five hours are needed to completely mineralize the dye and its intermediate. It is found that Fe2+ does not have significant influence on the reaction, while H2O2 could retard the reaction when its concentration is higher than 0.01 mM.

CdS dissolution and 2,4-dichlorophenol oxidation have been studied in the presence of thioacetamide during the photocatalytic reaction. It is interesting to find that both the organic oxidation and the degree of inhibition of CdS dissolution increase with increasing pH. In low pH range, the protonation of CdS surface is the major reason for CdS dissolution. Thioacetamide can inhibit the CdS dissolution to a certain degree only at the beganing of the first 8 hours. At high pH range, the formation of Cd(0H)2 determines the extent of CdS dissolution. The inhibition effect of thioacetamide on CdS has been minimized. The two proposed mechanisms have been confirmed by quantitative analysis of base consumption during the processes. The optimal light intensity is 700 watts and temperature was found to be not an important factor in CdS dissolution

Photocatalytic oxidation of 2,4-dichlorophenol (2,4-DCP) by CdS in the presence and absence of thioacetamide as a function of pH has been studied. Based upon the trends in the appearance of different intermediates such as benzene and hydroxylated biphenyl, it is proposed that 2,4-DCP oxidation by positive holes (h+) is favored at pH less than 6, while oxidation by hydroxyl radicals (·OH) becomes dominant at pH greater than 6. This is evidenced by the intermediates detected at different pH values. In the absence of thioacetamide (TA), benzene was detected as the only intermediate at pH ranging from 4 to 5. When pH changed from 5 to 9, no benzene was detected. Highly hydroxylated intermediates, such as hydroxylated biphenyl, were the major intermediates. When TA was present, it may act as a “bridge” between, 2,4-DCP and CdS through its thiol functional group. Therefore, a shift of the optimal pH for 2,4-DCP oxidation from 5 to 9 was observed and no hydroxylated biphenyl were detected.

In order to comply with the Urban Wastewater Treatment Directive's, Water Framework Directive's, Helsinki Commission and Estonian National Wastewater Treatment requirements to reveal the wastewater pressures and impacts on the receiving water, the aim of this work was to develop optimal Estonian Nutrient Discharge Standards for wastewater treatment plants. Wastewater treatment plants treatment efficiency, total pollution load coming from different size of treatment plants and feasibility for stricter treatment requirements and accompanying socio- economic impacts are evaluated with consideration of environmental benefits, brought by the investment. Limit values for small-scale (below 2000 population equivalent) treatment plants were proposed.

Three dye solutions, namely, C.I. Acid Yellow 17, C.I. Basic Blue 3, and C.I. Basic Red 2, were treated in an upflow anaerobic sludge blanket (UASB) reactor followed by a semi-continuous aerobic activated sludge tank. When hydraulic retention time was about 12 hours, no significant color removal was observed in the aerobic stage. In the anaerobic stage, Acid Yellow 17, Basic Blue 3, and Basic Red 2 were removed by 20%, 72%, and 78%, respectively. To treat wastewater from a dye manufacturing factory with COD concentration of 1200 mg/l and Color of 500 degree (dilution factor), an UASB reactor (4.5 liters) and an activated sludge tank (5 liters, adjustable), COD and color were removed by more than 83% and 90% at a COD loading rate of 5.3 kg COD/m3-day in the anaerobic stage, and at the hydraulic retention time of 6-10 hours for the anaerobic stage and 6.5 for the aerobic stage. The anaerobic stage of the A/O system removes both color and COD. In addition, it also improves biodegradability of dyes for further aerobic treatment.