Chemical Oxygen Demand Consumption Research Articles

Synergistic Integration of Anammox and Endogenous Denitrification Processes for the Simultaneous Carbon, Nitrogen, and Phosphorus Removal.

The feasibility of a synergistic endogenous partial denitrification-phosphorus removal coupled anammox (SEPD-PR/A) system was investigated in a modified anaerobic baffled reactor (mABR) for synchronous carbon, nitrogen, and phosphorus removal. The mABR comprising four identical compartments (i.e., C1-C4) was inoculated with precultured denitrifying glycogen-accumulating organisms (DGAOs), denitrifying polyphosphate-accumulating organisms, and anammox bacteria. After 136 days of operation, the chemical oxygen demand (COD), total nitrogen, and phosphorus removal efficiencies reached 88.6 ± 1.0, 97.2 ± 1.5, and 89.1 ± 4.2%, respectively. Network-based analysis revealed that the biofilmed community demonstrated stable nutrient removal performance under oligotrophic conditions in C4. The metagenome-assembled genomes (MAGs) such as MAG106, MAG127, MAG52, and MAG37 annotated as denitrifying phosphorus-accumulating organisms (DPAOs) and MAG146 as a DGAO were dominated in C1 and C2 and contributed to 89.2% of COD consumption. MAG54 and MAG16 annotated as Candidatus_Brocadia (total relative abundance of 16.5% in C3 and 4.3% in C4) were responsible for 74.4% of the total nitrogen removal through the anammox-mediated pathway. Functional gene analysis based on metagenomic sequencing confirmed that different compartments of the mABR were capable of performing distinct functions with specific advantageous microbial groups, facilitating targeted nutrient removal. Additionally, under oligotrophic conditions, the activity of the anammox bacteria-related genes of hzs was higher compared to that of hdh. Thus, an innovative method for the treatment of low-strength municipal and nitrate-containing wastewaters without aeration was presented, mediated by an anammox process with less land area and excellent quality effluent.

Bicarbonate Alternatives in the Neutralization Phase of Leather Tanning to Ensure Sustainability

The post-tanning procedure involves neutralizing the iso-electric point, which ensures that there is no imbalance between carboxylic groups and amino groups. This balance allows for the penetration of dyes, fatliquoring agents, and other chemical materials. Bicarbonate is used during the neutralization phase, and to eliminate it, 4 metric tons of water are needed for each metric ton of leather. Additionally, this leads to an elevation in both Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD). The objective of the research was to substitute bicarbonate with sodium borate, sodium acetate, and sodium formate, and neutralise syntan to decrease the quantities of pollutants generated from this process, minimize the consumption of water, and improve the quality of the produced leather. Each experimental group's BOD, COD, microscopic micrographs, physical, chemical, and organoleptic parameters were determined. The use of sodium borate, neutralizing syntan, sodium acetate, and sodium formate resulted in a significant decrease in the discharge of BOD, COD, and water consumption. Furthermore, the use of 2.5% sodium borate has proven to be the most effective neutralizing agent in reducing water consumption by 80%, total oxygen demand by 39% and costs of neutralization chemicals by 0.62%. Also, the physical and chemical properties of the leather product were similar to those of the control. Therefore, the leather that has been neutralized with sodium borate is considered to have the best organoleptic characteristics compared to the control.

Understanding the risk of using herbicides for tree root removal into wastewater treatment plant performance

Adding herbicides to sewer lines, a common practice for controlling root intrusion in sewer pipes, may adversely impact downstream wastewater treatment by inhibiting nitrification and denitrification performance. This study investigated the effects of herbicides, namely diquat, triclopyr, and 2-methyl-4-chlorophenoxyacetic acid (MCPA)-dicamba, on these processes. Various parameters were monitored, including oxygen uptake rate (OUR), nutrients (NH3–N, TP, NO3–N, and NO2–N), chemical oxygen demand (COD), and herbicide concentrations. It was found that nitrification was not affected by OUR in the presence of each herbicide at various concentrations (1, 10, and 100 mg L−1). Additionally, MCPA-dicamba at various concentrations demonstrated minimal inhibition in the nitrification process compared to diquat and triclopyr. COD consumption was not affected by the presence of these herbicides. However, triclopyr significantly inhibited NO3–N formation in the denitrification process at various concentrations. Similar to nitrification process, both COD consumption and herbicide reduction concentration were not affected by the presence of herbicides during the denitrification process. Adenosine triphosphate measurements showed minimal impact on nitrification and denitrification processes when herbicides were present in the solution up to a concentration of 10 mg L−1. Tree root kill efficiency experiments were performed on Acacia melanoxylon. Considering the performance on nitrification and denitrification process, diquat emerged as the best herbicide option (concentration of 10 mg L−1), with a 91.24% root kill efficiency.

Optimization and Operational Analysis of Domestic Greywater Treatment by Electrocoagulation Filtration Using Response Surface Methodology

Greywater is the most sustainable option to address the growing need for fresh water. This study aimed to identify the optimal operation variables of an electro-coagulation filtration (ECF) system for treating domestic greywater, using different conditions (e.g., different electrode combinations (Al-Fe-Al-Fe), initial pH (6.8–8.4), operating time (10–60 min), and voltage (6–24 volts)). A statistical data analysis was performed to evaluate the experimental conditions for modeling the chemical oxygen demand (COD), the total dissolved solids (TDSs), turbidity, and chloride removal effectiveness, almost ranging from (85 to 94%), respectively, with energy consumption using the response surface methodology (RSM) and the ANOVA test. When comparing the experimental and predicted model values, it was proved that the model fairly describes the experimental values with the R2 values determined >0.99 for COD, TDSs, turbidity, chloride, and energy consumption, suggesting a regression sustainability of the model. The sludge properties were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and FTIR spectroscopy, which indicated the removal of organic matter during the ECF, similar in composition, independently of the different applied voltage values used. The results of this study suggest the ECF significantly reduces the pollutants load in greywater, showing the aluminum-iron-based electrodes as a viable option to treat greywater with optimal operational costs ranging from (0.12 to 0.4) US$ m−3 under different voltage conditions and parameters. This study establishes a path for greywater treatment technology that is economical and environmentally responsible for wastewater management that leads to sustainability.

Nitrogen Removal from the High Nitrate Content Saline Denitration Solution of a Coal-Fired Power Plant by MFC

Oxidation denitration is one of the most efficient ways to remove NOx from flue gas in a coal-fired power plant. However, this oxidation denitration produces saline solution containing a high concentration of nitrate, which needs to be well treated. In this paper, MFC was firstly used to treat the high nitrate content saline denitration solution from ozone oxidation denitration of a coal-fired power plant. The influences of chemical oxygen demand (COD) and initial nitrate concentration on the nitrate removal and electricity generation of MFC were investigated by sequencing batch mode. The results showed that using MFCs could efficiently remove nitrate from coal-fired power plant saline denitration solution with nitrate nitrogen (NO3−-N) concentration up to 1510 mg/L. The average nitrate nitrogen removal rate was as high as 248.3 mg/(L·h) at initial nitrate nitrogen concentration of 745 mg/L and COD concentration of 6.5 g/L, which was eight times as high as that of the conventional biological method. Furthermore, the MFC required an average COD consumption of 3.42 g/g-NO3−-N which was lower than most of the conventional biological methods. In addition, MFC could produce a maximum power density of 241.1 mW/m2 while treating this saline denitration solution.

Treatment of wastewater using black soldier fly larvae, under different degrees of biodegradability and oxidation of organic content

The biological treatment process based on the metabolism of Black Soldier Fly (BSF) larvae proved to be a highly promising technique for the treatment of high organic content (HOC) wastewater, such as sewage from food industries, leachate from municipal solid waste (MSW) landfill, etc. The present study was aimed at achieving a better understanding of how biodegradability and degree of oxidation of organic content might influence treatment performance and biomass quality. Six leachates characterised by similar COD (Chemical Oxygen Demand) but different BOD5/COD (Biochemical Oxygen demand/COD) and TOC/COD (Total Organic Carbon/COD) ratios were tested. By combining these ratios, the BOD5/TOC ratio was introduced to take into account the effect of both leachate properties (biodegradability and oxidation degree). Process treatment performance was significantly influenced by the quality of organic substances. Higher BOD5/TOC values (higher biodegradability and lower oxidation degree) resulted in a greater and faster larvae growth, with final wet weight of between 49.2 and 91.9mg/larva; lower mortality between 5 and 32%; higher prepupation percentages ranging from 4 to 21% and higher specific substrate consumption rate with values varying from 0.051 to 0.063 mgTOC/mg larva/d, up to 3-fold higher than values obtained using conventional activated sludge based on COD consumption. Conversely, no significant differences were detected in larvae protein and lipid contents, including the profiling of fatty acids.

Hydrogen Production in Microbial Electrolysis Cells Based on Bacterial Anodes Encapsulated in a Small Bioreactor Platform.

Microbial electrolysis cells (MECs) are an emerging technology capable of harvesting part of the potential chemical energy in organic compounds while producing hydrogen. One of the main obstacles in MECs is the bacterial anode, which usually contains mixed cultures. Non-exoelectrogens can act as a physical barrier by settling on the anode surface and displacing the exoelectrogenic microorganisms. Those non-exoelectrogens can also compete with the exoelectrogenic microorganisms for nutrients and reduce hydrogen production. In addition, the bacterial anode needs to withstand the shear and friction forces existing in domestic wastewater plants. In this study, a bacterial anode was encapsulated by a microfiltration membrane. The novel encapsulation technology is based on a small bioreactor platform (SBP) recently developed for achieving successful bioaugmentation in wastewater treatment plants. The 3D capsule (2.5 cm in length, 0.8 cm in diameter) physically separates the exoelectrogenic biofilm on the carbon cloth anode material from the natural microorganisms in the wastewater, while enabling the diffusion of nutrients through the capsule membrane. MECs based on the SBP anode (MEC-SBPs) and the MECs based on a nonencapsulated anode (MEC control) were fed with Geobacter medium supplied with acetate for 32 days, and then with artificial wastewater for another 46 days. The electrochemical activity, chemical oxygen demand (COD), bacterial anode viability and relative distribution on the MEC-SBP anode were compared with the MEC control. When the MECs were fed with artificial wastewater, the MEC-SBP produced (at −0.6 V) 1.70 ± 0.22 A m−2, twice that of the MEC control. The hydrogen evolution rates were 0.017 and 0.005 m3 m−3 day−1, respectively. The COD consumption rate for both was about the same at 650 ± 70 mg L−1. We assume that developing the encapsulated bacterial anode using the SBP technology will help overcome the problem of contamination by non-exoelectrogenic bacteria, as well as the shear and friction forces in wastewater plants.

Electrocoagulation vs. Integrate Electrocoagulation-Natural Zeolite for Treatment of Biowaste Compost Leachate—Whether the Optimum Is Truly Optimal

Natural zeolites are well-known materials widely applied in the environmental remediation treatment process. However, the integration of various treatment methods is exceedingly investigated for achieving satisfactory effluent quality. In this paper, the integration of electrocoagulation and natural zeolite was evaluated in the treatment of biowaste compost leachate in a single step. The influence of different distances of electrodes (1.5, 3, and 4.5 cm), stirring speed (70, 200, and 400 rpm), the addition of natural zeolite and electrolyte NaCl on the efficiency of treatment of biowaste compost leachate has been carried out. Process efficiency was evaluated by measuring the change of pH value, electrical conductivity, temperature, turbidity, chemical oxygen demand (COD), total Kjeldahl nitrogen (TNK), total solids, and sludge settling test. The Taguchi method was applied to optimize biowaste compost leachate treatment. Experiments are planned according to Taguchi’s L8 (24 41) orthogonal array. The stirring speed, electrode distance, electrolyte and zeolite addition, solution initial pH adjustment were chosen as controllable factors, and their impact on COD, turbidity, TNK, settling rate, and electrode consumption were studied. Results show that optimal conditions depend on the parameter of interest and that optimal values for a particular parameter are not always the optimum if the desired goal is considered.

Impact of low temperature on ex situ nitritation/in situ denitritation in field pilot-scale landfill for postclosure care of leachate treatment and gas content.

Leachates and landfill gas (LFG) are the major problems for closed landfills (CL) and cause significant threats to receiving waterbody and ambient air quality. In this study, a field pilot-scale CL with ex situ nitritation/in situ denitritation process was constructed and operated continuously under wide temperature variations. The effect of low temperature on leachate treatment, and LFG content was studied. Results showed that the combined process can efficiently remove nitrogen and organic matters from leachate, and change LFG content under low-temperature condition. In the ex situ nitritaion, maximum removal efficiencies of ammonia and chemical oxygen demand (COD) were over 99% and 85%, respectively. The loading rate of nitrogen and COD reached 0.5kgNm-3 d-1 and 0.7kg COD m-3 d-1, respectively. The inhibitions of free ammonia (FA) and free nitrous acid (FNA), and low temperature were the key factors affecting nitritation. With recirculating nitrified leachate, total oxidized nitrogen (TON) was completely reduced, and the refuse decomposition was accelerated. Denitritation was the main reaction responsible in the CL. Additionally, methane content was observed lowly at non-inhibitory TON loading rate of 5.8±3.7gN ton-1 TS d-1. This decrease was not caused by the increased of TON loading, but a carbon source competition by denitrificans. The estimated COD consumption and methane reduction were 55.0kg d-1 by TON reduction, and 20m3 d-1, respectively. Hence, this study served a potential strategy for postclosure care of landfills under low temperature variation.

Comparative Study of Different Operation Modes of Microbial Fuel Cells Treating Food Residue Biomass.

Four multiple air–cathode microbial fuel cells (MFCs) were developed under the scope of using extracts from fermentable household food waste (FORBI) for the production of bioelectricity. The operation of the MFCs was assessed in batch mode, considering each cell individually. Τhe chemical oxygen demand (COD) efficiency was relatively high in all cases (>85% for all batch cycles) while the electricity yield was 20 mJ/gCOD/L of extract solution. The four units were then electrically connected as a stack, both in series and in parallel, and were operated continuously. Approximately 62% COD consumption was obtained in continuous stack operation operated in series and 67% when operated in parallel. The electricity yield of the stack was 2.6 mJ/gCOD/L of extract solution when operated continuously in series and 0.7 mJ/gCOD/L when operated continuously in parallel.

Treatment of healthcare wastewater using the peroxi-photoelectrocoagulation process: Predictive models for COD, color removal and electrical energy consumption

The peroxi-photoelectrocoagulation process was evaluated for the removal of chemical oxygen demand (COD) and color from healthcare wastewater. A 2-level full factorial design with center points was created to investigate the effect of the process parameters, i.e., initial COD, H2O2, pH, reaction time and current density. Furthermore, the total energy consumption and average current efficiency in the system were evaluated. Predictive models for % COD, % color removal and energy consumption were obtained. The initial COD and pH were found to be the most significant variables in the reduction of COD and color in peroxi-photoelectrocoagulation process. Hydrogen peroxide only has a significant effect on the treated wastewater when combined with other input variables in the process like pH, reaction time and current density. In the peroxi-photoelectrocoagulation process, current density appears not as a single effect but rather as an interaction effect with H2O2 in reducing COD and color. Lower energy expenditure was observed at higher initial COD, shorter reaction time and lower current density. The average current efficiency was found as low as 13 % and as high as 777 %. Overall, the study showed that hybrid electrochemical oxidation can be applied effectively and efficiently for the removal of pollutants from healthcare wastewater.

Enhanced treatment of landfill leachate wastewater using sono(US)-ozone(O3)–electrocoagulation(EC) process: role of process parameters on color, COD and electrical energy consumption

The combination of advanced oxidation processes (AOPs) and electrochemical process is gaining growing popularity for use in wastewater treatment. The present work explores for the first time, treatment of leachate wastewater from landfill waste using a combination of sonication (US), ozonation (O3) and electrocoagulation (EC) process expressed by % color removal, % Chemical Oxygen Demand (COD) removal and its associated electrical energy consumption. The results revealed that, the combined process (US/O3/EC) is highly successful in the treatment of leachate wastewater from landfill in terms of % color removal (100 %) and % COD removal (97.50 %) with low electrical energy consumption (8kWhr/m3) than the other hybrid and single process such as O3/EC, US/EC, US/O3 and EC, O3, US. The influence of different process parameters such as electrolyte concentration (1.50–7.50 g/L), current density (1.25–7.50 A/dm2), initial effluent pH (2–11), COD concentration (2000–6000 ppm), O3 production (0.75–3.75 g/hr) and sonication power (20–100 Watts) were studied on the efficiency of pollutant removal evaluated by reduction of % color and % COD and electrical energy consumption using hybrid US/O3/EC process. Overall, the analysis clearly showed that the approaches to integrated treatment technologies could synergistically remove the pollutant from the wastewater.

A 2.5D Electrode System Constructed of Magnetic Sb–SnO2 Particles and a PbO2 Electrode and Its Electrocatalysis Application on Acid Red G Degradation

A novel electrode consisting of a Ti/PbO2 shell and Fe3O4/Sb–SnO2 particles was developed for electrochemical oxidation treatment of wastewater. Scanning electron microscope (SEM), X-ray diffraction (XRD), the current limiting method, toxicity experiments, and high-performance liquid chromatography were adopted to characterize its morphology, crystal structure, electrochemical properties, the toxicity of the wastewater, and hydroxyl radicals. Acid Red G (ARG), a typical azo dye, was additionally used to test the oxidation ability of the electrode. Results indicated that the 2.5D electrode could significantly improve the mass transfer coefficient and •OH content of the 2D electrode, thereby enhancing the decolorization, degradation, and mineralization effect of ARG, and reducing the toxicity of the wastewater. The experiments revealed that, at higher current density, lower dye concentration and higher temperature, the electrochemical oxidation of ARG favored. Under the condition of 50 mA/cm2, 25 °C, and 100 ppm, the ARG, Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC) removal efficiency reached 100%, 65.89%, and 52.52%, respectively, and the energy consumption and the current efficiency were 1.06 kWh/g COD, 8.29%, and energy consumption for TOC and mineralization current efficiency were 3.81 kWh/g COD, 9.01%. Besides, the Fe3O4/Sb–SnO2 particles after electrolysis for 50 h still had remarkable stability. These results indicated that the ARG solution could be adequately removed on the 2.5D electrode, providing an effective method for wastewater treatment.

Performance improvement and model of a bio-electrochemical system built-in up-flow anaerobic sludge blanket for treating β-lactams pharmaceutical wastewater under different hydraulic retention time

This paper focused on the performance of an up-flow bio-electrochemical system (UBES) for treating the β-lactams pharmaceutical wastewater under different hydraulic retention time (HRT). UBES is added a bio-electrochemical system below the three-phase separator based on up-flow anaerobic sludge blanket (UASB). Comparisons of chemical oxygen demand (COD) removal, accumulation of volatile fatty acid (VFA) and biogas production were investigated during the 316-day operation time, which was divided into five parts with HRT of 96 h, 72 h, 48 h, 36 h and 20 h, respectively. The average COD removal efficiency of UBES could reach 45.3 ± 7.5%, 72.2 ± 3.5%, 86.2 ± 1.4%, 75.9 ± 1.8% and 64.9 ± 2.0%, which were 2.4%, 6.1%, 6.4%, 10.2%, 8.7% more than those of UASB under different HRTs, respectively. Biogas production as well as methane production of UBES were significantly higher than UASB during the whole changing HRT process, the maximum methane yield of UBES was 0.31 ± 0.07 L/gCODremoved. Accumulation of VFA in UBES was discovered to be lighter than UASB, the minimum average VFA in UBES was 131.9 ± 18.5 mg/L, which was obtained at HRT of 48 h. These results proved that UBES can slow down the inhibition of VFA on methanogens to make sure a good performance on COD removal and biogas production than UASB. Moreover, the relationships between methane production and VFA, biogas production and COD consumption were analyzed. A cost and benefit were analyzed for evaluating the potential of UBES in practical applications compared with UASB. Finally, radial basis function neural network (RBFNN) model was developed and fitted well with the experimental data, which can be employed to predict the effluent quality of the UBES and UASB.

Removal of organic pollutants from municipal wastewater by a horizontal pilot - scale constructed wetland utilizing Phragmites australis and Typha latifolia - Effectiveness monitoring per season

Constructed wetlands, as an alternative to conventional methods, are systemsdesigned on the basis of the application of natural purification processes that take placein watery and swampy overgrown habitats, with certain microbiological groups. In thewastewater treatment process various types of constructed wetlands can be combinedto achieve a higher efficiency of the purification.In this study, the removal effectiveness of the organic substances from municipalwastewater was monitored, using a horizontal pilot - scale constructed wetlandutilizing Typha latifolia and Phragmites australis. In addition to the measurement oforganic substances content through COD, BOD and KMnO4 consumption, and totaldissolved substances (TDS) in influent and effluent, microbiological sample analysis wasperformed, monitored by total number of coliform bacteria.The aim of this study was to calculate the effectiveness of removing organicsubstances from municipal wastewater, depending on the season, as well as theeffectiveness of eliminating total coliform bacteria.The results of one-year research have shown that the removal effectiveness ofthe organic substances from municipal wastewater, expressed as the chemical oxygendemand (COD), was the highest in summer - 87.82% ± 2.83%, and the lowest in thewinter - 64.51% ± 5.89%. During the study, effectiveness of elimination of total coliformbacteria was 97.88 ± 0.80% and total dissolved substances 71.27% .

Stable nitrite accumulation and phosphorous removal from nitrate and municipal wastewaters in a combined process of endogenous partial denitrification and denitrifying phosphorus removal (EPDPR)

In this study, a novel process was developed by combining endogenous partial denitrification (EPD, NO3−-N → NO2−-N) with denitrifying phosphorus removal (DPR) in an anaerobic/anoxic/aerobic sequencing batch reactor (SBR) to achieve a stable nitrite accumulation and phosphorus removal from high-strength nitrate (NO3−-N: 186.5 mg/L) and municipal wastewater (NH4+-N: 52.6 mg/L, chemical oxygen demand (COD): 242.7 mg/L). After 138-day, high nitrate-to-nitrite transformation ratio (NTR) of 75.3% and PO43−-P removal efficiency of 92.3% were achieved by controlling the anaerobic drainage ratio and anoxic/aerobic durations. During the anaerobic stage (2.5 h), carbon source in raw municipal wastewater was efficiently utilized by phosphorus-and-glycogen accumulating organisms (PAOs and GAOs) to enhance intracellular carbon storage (69.9% in anaerobic COD consumption), providing sufficient carbons for subsequent anoxic EPD and DPR. During the anoxic stage (2.5 h), high activity of DGAONO3-NO2 (denitrifying GAOs conducting NO3−-N → NO2−-N) over DPAONO3 and DGAONO3 (DPAOs and DGAOs conducting NO3−-N → N2) in nitrate denitrification (77.7% > 8.2% and 5.7%) facilitated the nitrite accumulation and phosphorus uptake. In the last short aerobic stage (10 min), further phosphorus was removed by aerobic PAOs without initiating ammonia/nitrite oxidation. Thus, effluent NO2−-N/NH4+-N ratio of 1.02:1 (close to the theoretical value of 1.32:1 for anammox process) with limited NO3−-N, PO43−-P and COD (1.8, 0.4 and 23.5 mg/L, respectively) were obtained. This provides the potential for advanced nutrient removal from nitrate and municipal wastewaters by combining EPDPR with anammox. Microbial community analysis revealed that Cluster I of Defluviicoccus-GAO group (∼7%) dominated the high nitrite accumulation performance, while Accumulibacter-PAO group (15 ± 3%) was responsible for the P removal performance.

Semi-continuous treatment of naphthenic acids using aerobic granular sludge

Process-affected water from the Canadian oil sands industry contains long chain cycloalkane carboxylic acids called naphthenic acids (NAs). The present proof-of-concept study aimed at assessing the shock response and treatability of commercial NAs using aerobic granular sludge (AGS) over 21 days. Mature aerobic granules were cultivated in a 5 L sequencing batch reactor (SBR) using synthetic acetate-based wastewater, and subjected to the NA mixture in three stages with varying organic loading rates. The introduction, starvation and the monitoring phases each had COD (chemical oxygen demand) removal efficiencies of 54.8%, 23.9% and 96.1%, and NA removal efficiencies of 71.8%, 43.3% and 67.0%, respectively. AGS biomass concentrations requiring higher COD consumption, and AGS surface area facilitating biodegradation and biosorption produced high specific removal rates. Specific COD removal rates ranged between 2678 and 6864 g COD/m3/d, whereas specific NA removal rates ranged between 0.5 and 12.2 g NA/m3/d. Supplemental nutrients were also degraded with over 90% removal efficiencies.

Microalgae-bacteria gas exchange in wastewater: how mixotrophy may reduce the oxygen supply for bacteria.

Microalgae-bacteria consortia application to wastewater treatment is considered as a potential and cheap strategy towards a self-sustaining oxygen-carbon dioxide gas exchange. However, microalgae can also carry out mixotrophy, thus reducing the net oxygen production, due to consumption of organic substrates. In this work, respirometric tests were used to quantify the oxygen reduction in the presence of biodegradable COD (chemical oxygen demand), which resulted up to 70%, depending on the biodegradability of the carbon substrate. The implication of mixotrophic metabolism on nutrient removal in urban wastewater was also measured by co-cultivating C. protothecoides with bacteria from activated sludge. To better understand the contribution of different populations, ad hoc experiments under controlled conditions were designed to quantify the nutrient consumption of bacteria and microalgae. Microalgae and bacteria were cultivated together and separately, with and without external bubbling, so to better ascertain the specific role of gas production and nutrient removal. Results showed that microalgae can remove up to 100 and 85% of P and N respectively, but the contribution on COD consumption may affect the net O2 supply to heterotrophic bacteria. However, a mutual COD consumption by microalgae and bacteria was proved by both experimental growth curves and mass balance application, based on stoichiometry experimentally adjusted.

Application of sulfate radicals from ultrasonic activation: Disintegration of extracellular polymeric substances for enhanced anaerobic fermentation of sulfate-containing waste-activated sludge

Sulfate radicals produced by ultrasonic activation of persulfate (PS) or sulfate were applied to disintegrate sludge flocs and extracellular polymeric substances (EPSs). The pretreatment facilitated the production of volatile fatty acids (VFAs) and hydrogen from subsequent anaerobic fermentation, yielding a potential method for improving the utilization of sulfate-containing waste-activated sludge (WAS). Sulfate radicals produced using ultrasound (US) in the presence of PS/sulfate showed a synergetic effect of advanced oxidation on WAS pretreatment. Among the three types of pretreatment (US, US + Sulfate, and US + PS), US + PS pretreatment was the most favoured for chemical oxygen demand (COD) solubilization, protein release, and sludge disintegration under a US density of 1.5 W/mL. Tightly bound EPS (TB-EPS) could be effectively disintegrated, and organic compounds were transformed into loosely bound EPS and soluble EPS. Unexpected COD consumption by excessive free radicals was also observed, when increasing the ultrasonic energy input (e.g. to 12 W/mL), towards a positive role for sludge disintegration and subsequent anaerobic fermentation. It was found that small particles (0.1–0.5 μm) from released organics could be preferentially overoxidized. An appropriate low ultrasonic strength initiated attack on the polymeric substances in WAS by the produced radicals, which TB-EPS could be primary target.

Combining partial nitrification and post endogenous denitrification in an EBPR system for deep-level nutrient removal from low carbon/nitrogen (C/N) domestic wastewater

In this study, partial nitrification and post endogenous denitrification (PED) were combined with enhancing bacterial phosphorus removal (EBPR) in an anaerobic/aerobic/anoxic operated sequencing batch reactor (SBR) for deep-level nutrient removal from low carbon/nitrogen (C/N, chemical oxygen demand (COD)/total nitrogen (TN)) domestic wastewater. At anaerobic stage, abundant organic matters (96.6% of COD consumption) in raw wastewater were stored as poly-hydroxyalkanoates (PHAs) by phosphorus and glycogen accumulating organisms with enhanced activities, which provided sufficient intracellular carbons for subsequent aerobic phosphorus uptake and anoxic PED. By controlling suitable aeration rate and duration, high nitrite accumulation rate (97.2%) was obtained at aerobic stage, which saved intracellular carbons consumption of PED. Moreover, the subsequent utilization of glycogen after PHAs via PED ensured the deep-level TN removal (94.9%) without external carbon addition. After 160-day operation, the average effluent PO43--P and TN concentrations were 0.4 and 3.0 mg/L, respectively, at C/N of 3.1.