Digester Effluent Research Articles

Insights into the carbon neutrality for the treatment process engineering of municipal wastewater by anaerobic membrane bioreactor integrated with partial nitritation-anammox: CO2 reduction and energy recovery

The promising sustainability and potential in carbon neutrality of the anaerobic membrane bioreactor (AnMBR) integrated with partial nitritation-anammox (PN/A) was assessed using a large pilot-scale plant. The entire pilot-scale system was conducted for a long-term continuous operation of 217 days, succeeding in the effective carbon-neutral treatment of low-strength real municipal wastewater with excellent COD removal efficiency of higher than 90 %. The major proportion of the organic matter was converted into bio-methane which can be recovered as bio-energy or bio-fuel. The residual ammonium contained in the digestate effluent of the AnMBR was further treated by a pilot-scale one-stage PN/A reactor. The long-term operation of the pilot-scale AnMBR was compared with the empirical assumption of the anaerobic-anoxic-oxic (A2/O) process, exhibiting splendid feasibilities in both ecological and economical perspectives including energy conservation and recovery, reduction of CO2 emission and electricity expenditure saving for municipal wastewater treatment. The application of AnMBR-PN/A process helps reducing the energy consumption of 0.416 kWh/m3 during the wastewater treatment process engineering of municipal wastewater, accounting for 90 % of that for the A2/O. The AnMBR-PN/A is also capable of reducing the CO2 emission reduced by 74.9 %. A full-scale wastewater treatment plant implemented with the AnMBR-PN/A process could save the electricity expenditure by 0.80 million CNY annually. The results of this work are solid evidence that the AnMBR-PN/A process is a remarkable sustainable technology, also giving new insights into the concept of carbon-neutral treatment of municipal wastewater in future studies.

PH-depended flushing in an automatized batch leach bed reactor system for volatile fatty acid production

In a two-stage CSTR system, the anaerobic digestion effluent from the second stage (methane reactor) can be used for pH-control in the acidification reactor. But using batch leach bed reactors, controlling the pH-value is key affecting factor due to dynamic process conditions. The aim of this work was to study, an automatized technical-scale leach bed reactor system for VFA-production with pH-dependent flushing. It was developed and tested at mesophilic and thermophilic operating conditions and compared to a time-controlled flushing mode. The reactors were fed with grass silage and the experiments were run for 35 days. Total cumulative VFA yields up to 270 g kg-1VS were achieved and extracted from the reactor. The methane formation in the leach bed reactors was successfully suppressed with a pH-controlled flushing mode. As a result of the extraction of the VFA from the leach bed reactors, the methane potential decreased by up to 50 %.

The sustainable utilization of anaerobic digestion effluents treating in suspended filler algae assisted systems

Significant amounts of anaerobic digestion effluents (ADE) containing high concentration of inorganic salts (source of nitrogen and phosphorus) and hardly degradable organic matter are produced during the generation of biogas using livestock manure. Without appropriate treatment, the imbalanced carbon to nitrogen ratio may lead to severe pollution of the environment. Considering different environmentally friendly processes such as recycling, energy regeneration, and sustainable development, suspended fillers were added to traditional algal-bacterial symbiosis (ABS) systems. In the present research, three systems including suspended filler algae assisted bio-reactor (SFA-PBR), no filler algae assisted bio-reactor (NFA-PBR), and single activated sludge system (ABS) were examined. Changes in bacterial communities were analyzed using high throughput sequencing. In addition, the mechanisms of ADE degradation in the presence and absence of suspended algae fillers were studied by comparing their effect on the degradation of COD (chemical oxygen demand), TN (total nitrogen), AN (ammonia nitrogen), and TP (total phosphorus). Systems where the ratio of active microalgae to bacteria was higher promoted the interaction between the two types of microorganisms, accelerating the stability of the ABS. Thus, the daily COD degradation rate in the stage was still high. Flora such as microalgae and bacteria were embedded in the filler spheres, which increased the microorganisms resistance to the poor environment induced by high concentrations of inorganic nutrients and organic matter present in the ADE. This favored the sustainable water utilization of ADE. After the treatment in the SFA-PBR system, the COD degradation rate was 75.32 %. The effluent COD concentration was 334.21 ± 39.18 mg/L. TN and AN degradation rates were 89.34 and 91.32%, respectively. The TN and AN concentrations in the effluent were 35.42 ± 2.65 and 29.97 ± 2.65 mg/L, respectively. The degradation rate of TP was 95.39 %. The effluent TP concentration was 0.86 ± 0.18 mg/L. The Chao diversity and ACE index values in the SFA-PBR system were higher than those of other groups. This result further supports the conclusion formulated with the Shannon diversity index result. Specifically, the effective sequence in the SFA-PBR system group presented a higher degree of homogeneity and abundance.

Water and green ammonia recovery from anaerobic digestion effluent by two-stage membrane distillation

A water and green ammonia recovery strategy for anaerobic digestion (AD) effluent treatment through a two-stage membrane distillation (2s-MD) was put forward in this study. In the 1st-stage, the MAP (monoammonium phosphate solution, NH4H2PO4)/DAP (diammonium phosphate solution, (NH4)2HPO4) loop, was used as the recyclable ammonia absorbent to recover ammonia from AD effluent. The multicycle ammonia absorption-regeneration experiments illustrated that the ammonia removal efficiency was stable (~81 %) and the recovered ammonia solution was 1.05 mol/L. In the 2nd-stage, the water recovery experiments from AD effluent with different ammonia concentrations were conducted. The results indicated that the water recovered from ammonia-removed AD effluent could be adopted as the general industrial or agricultural water. Finally, the economic evaluation demonstrated that the application of MAP solution as the recyclable ammonia absorbent was more economically efficient than the sulfuric acid solution. The treatment cost and net profit of AD effluent treatment by 2s-MD were $ 1.73/m3 and $ 0.83/m3, respectively. The 2s-MD can be acted as a valuable candidate strategy for sustainable green ammonia and water recovery from AD effluent.

Comparative Assessment of Nitrogen Concentration Effect on Microalgal Growth and Biochemical Characteristics of Two Chlorella Strains Cultivated in Digestate.

Microalgae have been recently recognized as a promising alternative for the effective treatment of anaerobic digestion effluents. However, to date, a widely applied microalgae-based process is still absent, due to several constraints mainly attributed to high ammonia concentrations and turbidity, both hindering microalgal growth. Within this scope, the purpose of the present study was to investigate the performance of two Chlorella strains, SAG 211-11b and a local Algerian isolate, under different nitrogen levels, upon ammonia stripping. The experiments were performed on cylindrical photobioreactors under controlled pH (7.8 ± 0.2) and temperature (25 ± 2 °C). Cultures were monitored for biomass production and substrate consumption. After sampling at the beginning of the stationary phase of growth (12th day) and after the maturation of the cells (24th day), an analysis of the produced biomass was conducted, in terms of its biochemical components. The local isolate grew better than C. vulgaris 211-11b, resulting in 1.43 mg L−1 biomass compared to 1.02 mg L−1 under 25 mg NH4-N L−1, while organic carbon and nutrient consumption varied between the two strains and different conditions. Concerning biomass quality, a high initial NH4-N concentration led to high protein content, while low nitrogen levels favored fatty acid (FA) accumulation, though the production of pigments was inhibited. In particular, the protein content of the final biomass was determined close to 45% of the dry weight in all experimental scenarios with adequate nitrogen, while proteins decreased, and the fatty acids approached 20% in the case of the local isolate grown on the substrate with the lowest initial ammonium nitrogen (25 mg NH4-N L−1). The novelty of the present work lies in the comparison of a microalga with industrial applications against a local isolate of the same species, which may prove to be even more robust and profitable.

Electrode-attached cell-driven biogas upgrading of anaerobic digestion effluent CO2 to CH4 using a microbial electrosynthesis cell

Upgrading biogas from anaerobic digestion (AD) has been highlighted as an alternative renewable energy source to replace geopolitically limited natural gas. The CO2 content of AD effluent is more than 40%, making it necessary to separate or increase the CH4 content to 95%. This study examined microbial electrosynthesis (MES) to convert CO2 directly to CH4 by a cathode electrode-attached cell. The MES with a −1.0 V (versus Ag/AgCl) applied cathodic potential exhibited a maximum methane production rate of 10.55 L CH4/m2 cat/day and achieved a 96% final CH4 content. Applying real biogas from a field AD plant resulted in a comparable production rate of 8.8L CH4/ m2 cat/ day with 95% CH4. The scaled-up bench MES reactor (total volume of 6L) was evaluated, and the energy efficiencies of the laboratory- and bench-scale MES were compared. The next-generation sequencing (NGS) revealed most methanogens (e.g., Methanobacterium, Methanothrix, and Methanobrevibacter) to be associated with the cathode surface rather than suspension. Cyclic voltammetry and field emission scanning electron microscopy showed that the electrode-associated cell predominantly controls the performance of the MES system. These results suggest that electrode-attached cells play a major role in the biogas upgrading of CO2 to CH4 in the MES system.

Characterising sedimentation velocity of primary waste water solids and effluents

Sedimentation in waste water is a heavily studied topic, but mainly focused on hindered and compression settling in secondary sludge, a largely monodispersed solids, where bulk sedimentation velocity is effectively described by functions such as double Vesilind (Takacs). However, many waste water solids, including primary sludge and anaerobic digester effluent are polydispersed, for which application of velocity functions is not well understood. These systems are also subject to large concentration gradients, and poor availability of settling velocity functions has limited design and computational fluid dynamic (CFD) analysis of these units. In this work, we assess the use of various sedimentation functions in single and multi-dimensional domains, comparing model results against multiple batch settling tests at a range of high and low concentrations. Both solids concentration and sludge bed height (interface) over time are measured and compared. The method incorporates uncertainty analysis using Monte Carlo regression, DIRECT (dividing rectangles), and Newton optimisation. It was identified that a double Vesilind (Takacs) model was most effective in the dilute regime (<1%v/v), but could not effectively fit high solids concentrations (>1%v/v) without a substantial (50%) decrease in effective maximum sedimentation velocity (V0). Other parameters (Rh, Rp) did not change. A power law velocity model (Diehl) was significantly less predictive at low concentrations, and not significantly better at higher concentrations. The optimised model (with reduction in V0) was tested vs a standard (optimised) double Vesilind velocity model in a simple primary sedimentation unit, and resulted in deviation from -12% to +18% in solids capture prediction from underload to overload (washout) conditions, indicating that the effect is important in CFD based analysis of these systems.

Changes in Organics and Nitrogen during Ozonation of Anaerobic Digester Effluent

The objective of this study is to investigate the consequence of ozone dosage rate on the qualitative change in organic compounds and nitrogen in anaerobic digester effluent during the ozone process. Therefore, ozonation improves the biodegradability of recalcitrant organic compounds, quickly oxidizes the unsaturated bond, and forms radicals that continue to deteriorate other organic matter. In this study, ozonation was performed in a microbubble column reactor; the use of microbubble ozone improves the status of chemical oxygen demand (COD) and changes of organic nitrogen to inorganic compounds. The ozone injection rates were 1.0, 3.2, and 6.2 mg/L/min. The samples obtained during the ozone treatments were monitored for CODMn, CODCr, TOC, NO2−-N, NO3−-N, NH4+-N, T-N, and Org-N. The ozone dose increased 1.0 to 6.2 mg/L and it increased the degradation ratio 40% and the total organic carbon 20% during 20 min of reaction time. During the ozonation, the CODCr and CODMn values were increased per unit of ozone consumption. The ozone treatment showed organic nitrogen mineralization and degradation of organic compounds with the contribution of the microbubble ozone oxidation process and is a good option for removing non-biodegradable organic compounds. The original application of the microbubble ozone process, with the degradation of organic compounds from a domestic wastewater treatment plant, was investigated.

Cultivation of microalgae in adjusted wastewater to enhance biofuel production and reduce environmental impact: Pyrolysis performances and life cycle assessment

The interest in microalgae as a renewable and sustainable feedstock for biofuels production has inspired a new focus in biorefinery. Current innovations in microalgae technology include the use of wastewater as the cultivation medium towards nutrients recovery, renewable energy generation, as well as wastewater treatment. Though recent studies have favoured the competitiveness of such an approach, how to maintain a high-quality microalgae-derived biofuel production in real wastewater with fluctuations in nutrient contents is still a challenge. This study investigated a strategy of adjusting the nutrient composition of the feeding wastewater (i.e. anaerobic digestion effluent) for microalgae cultivation (Desmodesmus sp.) and biofuel production. The addition of an appropriate amount of nutrients, including magnesium, iron and phosphorus, significantly enhanced the microalgal biomass production (0.78 g L−1) compared with the original wastewater (0.35 g L−1) and the standard BG11 microalgae cultivation medium (0.54 g L−1). In terms of the potential biofuel quality, the use of adjusted wastewater led to a higher content of valuable products (aliphatic hydrocarbon and fatty acids were accounted for 23.98% and 42.33% of the whole biomass, respectively) along with a reduction in potentially toxic substances (nitrogen-containing compounds and polycyclic aromatic hydrocarbons were accounted for 7.96% and 7.09% of the whole biomass, respectively) compared with the other cultivation groups. Moreover, the lower optimal temperature of pyrolysis engendered by the adjusted wastewater was significant for reduction of process energy consumption, which in turn led to overall lowered environmental impacts (838.52 mPET2000, applying life cycle assessment) than did the original wastewater (1165.67 mPET2000) and standard cultivation medium (1347.63 mPET2000). This study demonstrated that the adjustment of wastewater can act as a potential approach for the improvement in the quality of microalgal biofuel production, with consequent reduced environmental impacts.

Growth Characteristics of Chlorella sorokiniana in a Photobioreactor during the Utilization of Different Forms of Nitrogen at Various Temperatures.

The cultivation of microalgae requires the selection of optimal parameters. In this work, the effect of various forms of nitrogen on the growth and productivity of Chlorella sorokiniana AM-02 when cultivated at different temperatures was evaluated. Regardless of the temperature conditions, the highest specific growth rate of 1.26 day−1 was observed in modified Bold’s basal medium (BBM) with NH4+ as a nitrogen source, while the highest specific growth rate in BBM with NO3− as a nitrogen source achieved only 1.07 day−1. Moreover, C. sorokiniana grew well in medium based on anaerobic digester effluent (ADE; after anaerobic digestion of chicken/cow manure) with the highest growth rate being 0.92 day−1. The accumulation of proteins in algal cells was comparable in all experiments and reached a maximum of 42% of dry weight. The biomass productivity reached 0.41–0.50 g L−1 day−1 when cultivated in BBM, whereas biomass productivity of 0.32–0.35 g L−1 day−1 was obtained in ADE-based medium. The results, based on a bacterial 16S rRNA gene sequencing approach, revealed the growth of various bacterial species in ADE-based medium in the presence of algal cells (their abundance varied depending on the temperature regimen). The results indicate that biomass from C. sorokiniana AM-02 may be sustainable for animal feed production considering the high protein yields.

Restoring River Water Pollution from the Impact of Water Hyacinth (Eichornia crassipes) through Utilization as Raw Material for Fertilizer

Water hyacinth is an invasive foreign plant that is very detrimental to life in a habitat, as well as destroying the structure of an ecosystem and ultimately controlling all existing habitats. The negative impact is on the socio-economic aspects. How to control that can be done: Physical control such as pulling, digging, or using tools to uproot and cut plants burning, Chemical control using herbicides, restoration by means of revegetation and reintroduction of the desired natural plant or vegetation species. The aim of this research is the sanitation of river water by utilizing water hyacinth plants as fertilizer. The study design was one group post test design. The research was conducted by taking samples in Bening Reservoir (PT.Jasa Tirta): Pajar Village, Saradan District, Madiun Regency, East Java. The research was carried out in the Laboratory of D-III Environmental Health Magetan Poltekkes of the Ministry of Health, Surabaya and the Laboratory of Soil Science, Faculty of Agriculture, Sebelas Maret University, Surakarta. The research was carried out with treatment for: 7 days, 14 days and 21 days by measuring: Micro nutrient elements. set and the pH at the end of the observation. Treatment activities and variations in research dosages were as follows: The number of research samples was: 6 samples with research parameters for micro nutrients: Fe, Mn, Zn and pH. The sampling technique is Simple Random Sampling. Tools used ; A set of fermentation tools in the form of a bucket with a lid equipped with a wooden stirrer, measuring cup and scale. The research materials include: biogas effluent digester (raw material for fertilizer), fermentation bacteria/fermenter (EM-4), molasses and water. Data were collected by conducting laboratory examinations of samples sent and examined with micro nutrient parameters according to variations in observation time. Data analysis was carried out by comparing the requirements for organic fertilizers. Minimum Technical Requirements for Organic Fertilizer, Biofertilizer and Soil Improvement. All micro nutrient parameters (Fe, Mn, Zn and pH) are in accordance with the required standards for fertilizers. The results of the study of micro nutrients (Fe) obtained results: 192 ppm, without treatment as a control decreased to: 66.86 ppm, Mn nutrients, without treatment: 119.46 ppm, Zn analysis results, without treatment: 9.92 ppm, pH parameters have met the requirements, namely between 4-9 while the results of laboratory tests are in the range of 6.96 - 7.93. The results of the research on the treatment with the addition of EM-4 and Molasses with fermentation time of 7, 14 and 21 days, there was a decrease in the quality of micro nutrients, not according to the quality standards of liquid fertilizers. The conclusion of the results of this study is that the micro nutrient content before treatment (Fe, Mn, Zn) and pH, it turns out that some have met the requirements according to the Ministry of Agriculture, except that Zn nutrients are still below the standard. Micro nutrient content after treatment week 1 to week 3 and control, the nutrients (Fe, Mn, Zn) and pH were still below without treatment. The effluent of the biogas digester as raw material for water hyacinth without any treatment has met the requirements as an organic fertilizer as long as its use has exceeded 60 days in the digester.

Effects of Different pH Control Strategies on Microalgae Cultivation and Nutrient Removal from Anaerobic Digestion Effluent.

This study investigated nutrient removal from anaerobic digestion effluent by cultivating mixed-culture microalgae enriched from anaerobic sludge under different pH conditions: RUC (uncontrolled), R7–8 (maintained at 7–8), and R<8 (maintained below 8). Significant amounts of NH4+-N were lost by volatilization in RUC cultures due to increased pH values (≤8.6) during the early period of cultivation. The pH control strategies significantly affected the biological NH4+-N removal (highest in R7–8), microalgal growth (highest in R7–8), biomass settleability (highest in R<8), and microalgal growth relative to bacteria (highest in R<8) in the cultures. Parachlorella completely dominated the microalgal communities in the inoculum and all of the cultures, and grew well at highly acidic pH (<3) induced by culture acidification with microalgal growth. Microalgae-associated bacterial community structure developed very differently among the cultures. The findings call for more attention to the influence and control of pH changes during cultivation in microalgal treatment of anaerobic digestion effluent.

Responses of Coagulant Type, Dosage and Process Conditions to Phosphate Removal Efficiency from Anaerobic Sludge.

Phosphorus, a crucial component of life, may cause eutrophication if it is discharged untreated into the aquatic ecosystem. Phosphate (PO43-) may exist at an elevated level in anaerobic digestion (AD) effluents and can lead to the clogging of pipes by forming struvite crystals. This study was conducted to assess the responses of coagulant type, dosage and process conditions to phosphate removal efficiency from anaerobic sludge. The experiments were performed in two steps. First, a sensitivity test was conducted to compare five coagulant types (alum, poly-aluminum chloride (PAC), FeCl2, FeCl3 and PAC + FeCl3) at standard coagulation conditions. The results showed that PAC would be the best coagulant among the tested, while a combination of PAC and FeCl3 may be beneficial under circumstances. Second, an optimization study was performed for PAC using response surface methodology employing central composite design. Among the three independent variables (coagulant dosage, slow mixing duration and agitation speed), the dosage was the sole significant variable for phosphate removal efficiency, while the other two had limited effects. A future study to optimize the rapid mixing conditions would give additional insights into the process. The results of this study may be useful to design a process to counteract phosphate discharges from AD plants, as well as to reduce the risks of pipe clogging and maintenance problems due to crystalline struvite formation in the later stage of AD.

Effect of pH on Schizochytrium limacinum Production Grown Using Crude Glycerol and Biogas Digestate Effluent

The ability of microalgae, such as the rich in docosahexaenoic acid (DHA) heterotrophic marine microalgae Schizochytrium limacinum SR21, to utilize nutrients in their culture media derived from low-cost nutrient sources makes them a promising low-cost alternative source for the production of useful substances used in aqua feeds. The assessment of culture parameters, one of which is the pH, for every different nutrient growth medium used for microalgae cultivation is important, as they affect the biomass and secondary metabolite microalgae production. This study assessed the effect of different growth medium pH levels (6, 7, 8 and 9), at laboratory and pilot scale systems, on S. limacinum biomass productivity, lipid accumulation, proximate composition, carbon assimilation and DHA. The microalgae were cultivated in growth media containing two different alternative low-cost nutrient sources: (a) crude glycerol derived from biofuel industry as carbon source and (b) effluent digestate from biogas production of livestock decomposition as a source of nutrients and trace elements. It was found that a neutral pH (7) was the optimum level, as it enhanced biomass productivity of the lab and pilot scale cultivation systems at 44.9 g L−1 and 11 g L−1 and DHA content at 7.5% and 19% of the total lipid content, respectively.

Assessment of Nutrients Recovery Capacity and Biomass Growth of Four Microalgae Species in Anaerobic Digestion Effluent

Four microalgae species were evaluated for their bioremediation capacity of anaerobic digestion effluent (ADE) rich in ammonium nitrogen, derived from a biogas plant. Chlorella vulgaris, Chlorella sorokiniana, Desmodesmus communis and Stichococcus sp. were examined for their nutrient assimilation efficiency, biomass production and composition through their cultivation in 3.7% v/v ADE; their performance was compared with standard cultivation media which consisted in different nitrogen sources, i.e., BG-11NO3 and BG-11ΝH4 where N-NO3 was replaced by N-NH4. The results justified ammonium as the most preferable source of nitrogen for microalgae growth. Although Stichococcus sp. outperformed the other 3 species in N-NH4 removal efficiency both in BG-11NH4 and in 3.7% ADE (reaching up to 90.79% and 69.69% respectively), it exhibited a moderate biomass production when it was cultivated in diluted ADE corresponding to 0.59 g/L, compared to 0.89 g/L recorded by C. vulgaris and 0.7 g/L by C. sorokiniana and D. communis. Phosphorus contained in the effluent and in the control media was successfully consumed by all of the species, although its removal rate was found to be affected by the type of nitrogen source used and the particular microalgae species. The use of ADE as cultivation medium resulted in a significant increase in carbohydrates content in all investigated species.

Microalgae production for nitrogen recovery of high-strength dry anaerobic digestion effluent

Dry anaerobic digestion (D-AD) generates nitrogen-rich effluents that are normally neglected in the circular bioeconomy. The high turbidity and ammonium content hamper nitrogen recovery from these effluents via biological processes, such as microalgae culture. The goal of this study was to demonstrate microalgae growth viability in high-strength D-AD effluents in order to recover nitrogen (N) as microalgae biomass. According to the experimental factorial design conducted in batch reactors, ammonium was identified as the critical inhibitory compound for microalgae growth while turbidity did not exhibit a significantly negative effect. Instead, turbidity resulted advantageous since it promoted high nitrogen uptake rates and biomass production. The presence of organic turbidity resulted in a positive effect that boosted Chlorella growth in a stream with higher ammonium (350 mg NH4+-N L-1) and turbidity (175 NTU) than the inhibition thresholds reported in the literature, reaching 98.7% of N recovery as microalgae biomass. When microalgae culture was scaled up in a photobioreactor operated in continuous mode, microalgae biomass was effectively produced while recovering 100% of N at a hydraulic retention time of 10 days. By imposing long exposure times and high turbidity, Chlorella adaptation to high-strength D-AD effluent resulted in high N uptake and biomass production. This study demonstrated not only the most influencing factor and the optimal NH4+-N and turbidity combination, but also the viability of using D-AD effluents as culture media for microalgae biomass production.

Effects of oxytetracycline and zinc ion on nutrient removal and biomass production via microalgal culturing in anaerobic digester effluent

Removal of nutrients from swine wastewater digester effluent (SWDE) by microalgae Coelastrella sp. and production of Coelastrella sp. were investigated at the presence of oxytetracycline (OTC) and Zn(II). Mechanisms of stress of OTC and Zn(II) on microalgae were discussed via analyzing the removal performance of SWDE and biochemical characteristics of microalgae. Results showed that removal efficiency of ammonia nitrogen and biomass yield of microalgae at the presence of 5000 μg/L of OTC decreased by 13.1% − 50.1% and 28.2% −71.5%, respectively, when Zn concentration was increased from 0.50 mg/L to 5.0 mg/L. The presence of 5.0 mg/L Zn(II) promoted the accumulation of lipids in microalgae, and the presence of 50 μg/L OTC increased unsaturation of fatty acid methyl ester. Content of glutathione and activity of both glutamine synthetase and superoxide dismutase decreased with the increase of OTC concentration, while content of adenosine triphosphatase increased when Zn(II) concentration was also increased.

Electro-Oxidation of Anaerobic Digester Effluent Results in Solids Separation by Electro-Flotation Combined with COD and Ammonia Oxidation

Electro-Oxidation of Anaerobic Digester Effluent Results in Solids Separation by Electro-Flotation Combined with COD and Ammonia Oxidation

Phosphate recovery from anaerobic digestion effluent using synthetic magnetite particles

Many researchers studied for phosphate recovery, but practical approach through scale-up still remains a challenge. Therefore, we present a technology for recovery of phosphate in anaerobic digestion effluent by synthesizing magnetite. The zeta potential, Fourier transform infrared spectroscopy (FT-IR), and X-ray Photoelectron Spectroscopy (XPS) analyses were used to derive the phosphate adsorption mechanism of magnetite. Physical adsorption is a weak bond generated by electrostatic attraction on the magnetite surface, and chemical adsorption occurs by ligand exchange in which OH- bonded to the magnetite surface is replaced with H2PO3-. The pseudo-second-order kinetics (R2 > 0.9999) and Langmuir-Freundlich model (R2 > 0.9999) were most suitable for phosphate adsorption. Magnetite follows both Langmuir and Freundlich adsorption isotherms, the phosphate adsorption characteristics by adsorption isotherm is consistent with the zeta potential, XPS and FT-IR analysis. In addition, it was confirmed that magnetite is a stable adsorbent when operating phosphate recovery processes for sewage through adsorption, desorption, and reuse.

Relationship between ultraviolet-visible spectra and soluble species in the liquid phase of wastewater sludge during biological digestion under mesophilic and thermophilic conditions

Absorption of ultraviolet (UV)-visible (Vis) light by the liquid phase of wastewater sludge during biological digestion was studied. Sludge samples were obtained from batch anaerobic and aerobic digestion experiments conducted at mesophilic and thermophilic temperatures, as well as influent and effluent of a full-scale anaerobic digester. In tandem with acquiring the UV-Vis spectra, the concentration of soluble parameters was measured. Integrated areas under the spectra in the UV and Vis regions were calculated as AUV and AVis, respectively. For the batch experiments, the computed areas increased with digestion time. In addition, a power-law function was able to describe the correlation between soluble chemical oxygen demand (SCOD) concentration and AUV for anaerobic digestion at 35 °C and 45 °C, and aerobic digestion at 55 °C. Coefficients of determination (R2) for the mentioned cases were between 0.812 and 0.933. Furthermore, power-law functions also described a correlation between SCOD and soluble ortho-phosphate concentrations during batch anaerobic digestion at 35 °C (R2 = 0.921) and 45 °C (R2 = 0.812). Moreover, analysis of the data obtained from the aerobic digestion experiment suggests that the mass of UV-absorbing matter linearly decreased over time during aerobic digestion at 45 °C (R2 = 0.925) and 55 °C (R2 = 0.996). The outcomes of the current study indicate that the integrated area under the UV spectrum of sludge filtrates reflects the progression of biological digestion of wastewater sludge under thermophilic and mesophilic conditions, which can be used for process monitoring and optimization.