Soluble Chemical Oxygen Demand Concentration Research Articles

Multiomics study on co-fermentation of chemically enhanced sludge and waste activated sludge to produce volatile fatty acids under different temperatures and pHs

This study examined the effects of different temperatures (37°C and 45°C) and pH (uncontrolled, 8 and 10) on the co-fermentation of FeCl3, anionic polyacrylamide (a-PAM) settling chemical enhanced primary sedimentation (CEPS), and waste activated sludge (WAS) to produce volatile fatty acids (VFAs), which analyzed through characterization, microbial community, and untargeted metabolic pathways. Further, to investigate the interacting effects, temperatures of 37°C, 45°C, and pHs of 8 and 10 were chosen, with a sludge ratio of 7.5. The hydrolysis of sludge was aided by the concentration of soluble chemical oxygen demand (SCOD) rising as temperature and pH rose. Nevertheless, elevated SCOD concentrations failed to materialize into benefits for acid production. Therefore, considering practical applications, the optimal conditions for acid production were determined to be 37°C and pH 10, with a concentration of 3411.17 ± 119.92 mg COD/L. A thorough investigation of correlations between microbial communities, differential metabolites, and environmental factors was carried out, highlighting the significance of pH in relation to microbial and acid production performance. That instance, the pH affects acid generation efficiency more so than temperature parameters. Within the microbial community, there is a considerable positive correlation between several distinct metabolites and Steptococcus, Trichococcus, and Tepidimimicrobium. These metabolites are intimately associated with the materials and energy needed for biological cell production and metabolism. This could be as a result of how environmental influences alter the distribution of microbial populations, which influences various metabolites and ultimately the process of producing acid.

Biodegradability and bioavailability of dissolved substances in aquaculture effluent: Performance of indigenous bacteria, cyanobacteria, and green microalgae

Aquaculture is a controlled aquatic farming sector and one of the most important human food sources. Fish farming is one of the predominant, fast-growing sectors that supply seafood products worldwide. Along with its benefits, aquaculture practices can discharge large quantities of nutrients into the environment through non-treated or poorly treated wastewater. This study aims to understand the nutrient composition of fish wastewater and the use of indigenous bacteria, cyanobacteria, and microalgae as an alternative biological treatment method. Wastewater samples from a local fish farming facility were collected and treated using six different species of cyanobacteria and microalgae include Chroococcus minutus, Porphyridium cruentum, Chlorella vulgaris, Microcystis aeruginosa, Chlamydomonas reinhardtii, and Fischerella muscicola. All the samples were incubated for 21 days, and the following parameters were measured weekly: Chemical oxygen demand (COD), phosphate, total dissolved nitrogen, and dissolved inorganic nitrogen. In addition, dissolved organic nitrogen (DON), bioavailable DON (ABDON), and biodegradable DON (BDON) were calculated from the mass-balance equations. Colorimetric and digestive methods were used for the parameter measurements. The results showed that C. reinhardtii reduced the soluble COD concentration by 74.6 %, DON by 94.3 %, and phosphorous by more than 99 %. Moreover, M. aeruginosa, and C. minutus significantly reduced inorganic nitrogen species (>99 %). This alternative fish wastewater treatment method was explored to gain insight into fish wastewater nutrient composition and to create a sustainable alternative to conventional fish wastewater treatment methods.

Effect of Orifice Induced Hydrodynamic Cavitation on the Properties of Waste Activated Sludge

Exploring alternative methods to reduce the quantity of wastewater sludge and improve its characteristics is among the prioritized subjects in the field of sludge management. Hydrodynamic cavitation, commonly employed for water and wastewater treatment, also holds the potential for utilization as a pre-treatment method for sludge. In the presented study, the excess sludge obtained from the wastewater treatment facility of a food and beverage manufacturing factory was collected and disintegrated with a orifice-induced hydrodynamic cavitation unit. According to the data obtained, the highest cavitation performance was achieved under the condition where the cavitation number was set to 0.3. In addition, hydrodynamic cavitation performed under the optimum operating conditions, significantly increased the solubility of waste activated sludge. The results showed that the soluble chemical oxygen demand concentration, which was initially determined as 382 mg/l, reached 3,068 mg/l end of the cavitation. 64% of the total Kjeldahl nitrogen and 60% of the total phosphorus of waste-activated sludge were converted into soluble forms by the effects of hydrodynamic cavitation. Moreover, the results of the microbial study indicated that removal rates of indicator bacteria varied between 94% and 99%.

Effect of extracellular polymeric substances removal and re-addition on anaerobic digestion of waste activated sludge

Extracellular polymeric substances (EPS) play a key role in anaerobic digestion of excess sludge. The influence of EPS removal and re-addition on sludge anaerobic digestion were investigated by batch experiment. The results showed that both EPS removal and re-addition improved sludge anaerobic digestion, the cumulative methane production increased by 14.9 % and 50.4 %. EPS removal promoted sludge hydrolysis and acidification, the soluble chemical oxygen demand (SCOD) and volatile fatty acids (VFAs) concentration increased by 31 % and 29 %. The re-addition of EPS increased the substrate of sludge fermentation, resulting in 1.64 and 1.77 times higher SCOD and VFAs concentration than that of control group. In addition, EPS contained lots of electrochemically active substances, and re-adding EPS increased the electron transfer system activity in anaerobic digestion by 164 %, which enhanced significantly methane production. Both removal and re-addition of EPS altered the microbial community structure in anaerobic digestion, the bacteria with hydrolysis and acidification functions were enriched, such as Chloroflexi and Desulfobacterota. Methanobacterium and Methanosaeta were the dominant methanogens in anaerobic digestion systems, and their relative abundance were increased by removing and re-adding EPS.

Effect of predatory bacterial mixtures on biolysis of waste activated sludge to improve dewatering performance

ABSTRACTThe generation of surplus sludge during biological wastewater treatment has become a prevalent issue, necessitating the development of a dewatering approach that is efficient, economically feasible, and ecologically sound. Bdellovibrio-and-like-organisms (BALOs) are obligatory parasitic bacteria that prey on an array of bacteria. In this study, different BALO strains were isolated and purified from waste activited sludge (WAS). Anti-predation host strains were applied to screen the BALO strains with different host-range to minimize the overlap of the biolysis prey spectrum. In addition, the BALO strains with different host preferences were mixed for sludge biolysis treatment efficiency comparison. The results indicated that the capillary suction time and the bound water content in the WAS treated with the mixed BALOs were significantly decreased by 25.9% ± 1.7% and 5.2% ± 1.2%, respectively, compared to those treated with the single BALO strain. The soluble chemical oxygen demand concentration in the mixed BALOs treated group was increased by 31.2% ± 0.7% than that treated with the single strain. The findings indicate that the mixed strains used in the treatment process resulted in a notable enhancement of both sludge dewatering performance and lysis degree. In addition, the abundance of Proteobacteria treated with the BALO mixtures decreased by 69.1% than the single strain treated one which demonstrated that the BALO mixture expanded the sludge host lysis spectrum. This study revealed the different effects of single and mixed strains on sludge community structure, suggesting that the BALO host-range expansion is crucial to further improve sludge dewatering performances.

Acidogenic Fermentation of Kitchen Waste for the Production of Volatile Fatty Acids: Bioaugmentation by Bacillus GIEC

In this study, the lignocellulosic (banana peel, tea residue, and paper towel in a ratio of 1:1:1) and protein (chicken breast) components of kitchen waste (KW) were used as substrates for mesophilic anaerobic fermentation to produce volatile fatty acids (VFAs). The ability of a new strain belonging to Bacillus sp. to improve the degradation of kitchen waste and VFAs production was investigated. The results showed that the addition of Bacillus cell wall depolymerization GIEC (Bacillus GIEC) to the fermentation system could result in higher concentrations of soluble chemical oxygen demand (sCOD), improved the removal rates of volatile solids (VS), and increased yield of VFAs from the substrates. Compared with the control group, the sCOD concentrations of lignocellulosic and protein substrates increased by 132.58% and 18.36%, respectively; the volatile solids removal rates of lignocellulosic and protein substrates increased by 84.96% and 135.53%, respectively; the yield of VFAs of lignocellulosic and protein substrates increased by 61.29% and 35.92%, respectively, reaching 0.31 g/g VSadded and 0.67 g/g VSadded, separately. According to the study, the addition of Bacillus GIEC enhanced the solubilization of solid organic matter during hydrolysis process, further resulting in a higher yield of VFAs compared to the control group. Furthermore, the micro-aerobic test showed that the bioaugmentation ability of Bacillus GIEC has little effect by the presence of oxygen. The Bacillus GIEC has the potential for bioaugmentation of the VFAs production from kitchen waste.

Effect of pretreatment with alkali on the anaerobic digestion characteristics of kitchen waste and analysis of microbial diversity

Abstract Kitchen waste contains high contents of organic matter and moisture, and it is prone to biodegrade and decompose to give odors. If not collected and transported promptly or treated improperly, it is highly likely to pollute the environment and spread diseases. Because the lipid content in kitchen waste is high and a portion of organic matter is not subject to hydrolysis, the development of anaerobic digestion technology has been greatly limited. Kitchen waste was pretreated with NaOH, KOH, and Ca(OH)2 with different concentrations, and 50 days sequencing batch mesophilic anaerobic digestion experiments were conducted. This study sheds light on the pollution reduction and energy generation of kitchen waste. The results are as follows: (1) The lipid content of kitchen waste could be reduced, and the concentration of dissolved organic matter could be increased by pretreating with alkali. The degradation rate of kitchen waste lipid reached a maximum of 50.51%, if 3% NaOH was added, and the soluble chemical oxygen demand concentration was increased by 235.3%. (2) The cumulative methane (CH4) output and biogas production efficiency were improved in the anaerobic digestion process with kitchen waste pretreated with alkali. The maximum daily gas output of kitchen waste pretreated with NaOH and KOH took place on the 11th to 12th day, with the biogas production efficiency of 40.4 and 45.2 mL·g·VS−1. The cumulative CH4 output was increased from 370.2 mL·g·VS−1 (untreated) to 393.1 and 434.1 mL·g·VS−1, respectively. In addition, the concentration of CH4 in biogas was increased from 54.8% (untreated) to 59.1% and 61.7%, respectively. (3) The Chao1 and Ace values of bacteria were increased first and then decreased. On the 10th day, the diversity of bacteria reached the highest value, and on the 20th day, the diversity of archaea reached its maximum. Therefore, it was verified that the improvement in the hydrolysis acidification efficiency and degree was crucial for the rapid and complete anaerobic digestion reactions.

Anaerobic digestion of waste activated sludge to produce volatile fatty acids and release nutrients using sodium citrate with sodium hydroxide pretreatment

AbstractThis study investigated the synergistic effect of sodium citrate (SC) and sodium hydroxide (NaOH) on the anaerobic digestion (AD) efficiency of waste activated sludge (WAS). Using the amount of SC as the control variable, changes in sludge cell cracking and AD performance under different pretreatment conditions was investigated. The optimum treatment conditions were a NaOH input of initial pH 10 and an SC concentration of 0.20 g/g total suspended solids. The pretreatment was monitored in 150 min. And the changes in soluble chemical oxygen demand (SCOD), soluble polysaccharide, soluble protein, volatile fatty acids (VFAs), PO43−‐P and NH4+‐N during the pretreatment stage and fermentation process were studied. Results show a significant disintegration effect on WAS under optimal pretreatment conditions, with the peak concentration of SCOD, soluble protein, and soluble polysaccharide being 2059.5, 114.86, and 190.97 mg/L, respectively, which means that large amounts of intracellular carbon sources were released. The production of VFAs included acetic acid, propionic acid, isobutyric acid, n‐butyric acid, isovaleric acid, and n‐valeric acid, with a peak concentration of 9555.89, 1779.12, 608.84, 805.7, 777.91, 184.86 mg·COD/L, respectively. The content of PO43‐P and NH4+‐N were great in fermentation liquid, 71.82 and 320.75 mg/L, respectively. These results indicate that the synergistic process improve VFAs production and contribute to nutrients reuse.

Intermittent Microaeration Technology to Enhance the Carbon Source Release of Particulate Organic Matter in Domestic Sewage

Domestic sewage treatment plants often have insufficient carbon sources in the influent water. To solve this problem, the commonly used technical means include an additional carbon source, primary sludge fermentation, and excess sludge fermentation, but these methods are uneconomical, unsustainable, and not applicable to small-scale wastewater treatment plants. Intermittent microaeration technology has the advantages of low energy-consumption, ease of application, and low cost, and can effectively promote anaerobic digestion of municipal sludge; however little research has been reported on its use to enhance the carbon sources release of particulate organic matter (POM) from domestic wastewater. Therefore, the effect of intermittent microaeration on the carbon source release of POM was evaluated in this study, with POM as the control test. The results showed that the release concentration of soluble chemical oxygen demand (SCOD) was the highest on day 4 under microaerobic conditions, and the concentrations of SCOD, NH4+-N, and PO43−-P in the liquid phase were 1153, 137.1, and 13 mg/L, respectively. Compared with the control group, the SCOD concentration increased by 34.2%, and the NH4+-N and PO43−-P concentrations decreased by 18.65% and 17.09%, respectively. Intermittent microaeration can effectively promote the growth of Paludibacter, Actinomyces, and Trichococcus hydrolytic fermentation functional bacteria. Their relative abundances increased by 282.83%, 21.77%, and 23.47%, respectively, compared with the control group. It can simultaneously inhibit the growth of acetate-type methanogenic archaea, Methanosaeta and Methanosarcina, with a decrease in relative abundances of 16.81% and 6.63%, respectively. The aforementioned data show that intermittent microaeration can not only promote the hydrolysis of POM, but can also reduce the loss of acetic acid carbon source, which is a cost-effective technical way to enhance the release of a carbon source of particulate organic matter in domestic sewage.

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.

The Pilot Study of the Influence of Free Ammonia on Membrane Fouling during the Partial Nitrosation of Pig Farm Anaerobic Digestion Liquid.

The problem of membrane fouling is a key factor restricting the application of the membrane bioreactor (MBR) in the partial nitrosation (PN) and anaerobic ammonia oxidation (anammox) processes. In this study, the pilot-scale continuous flow MBR was used to start up the partial nitrosation process in order to investigate the change trend of mid-transmembrane pressure (TMP) in the process of start-up, which was further explored to clarify the membrane fouling mechanism in the pilot-scale reactor. The results showed that the MBR system was in a stable operating condition during the partial nitrosation operation and that the online automatic backwash operation mode is beneficial in alleviating membrane fouling and reducing the cost of membrane washing. Particular attention was paid to the influence trend of free ammonia (FA)on membrane fouling, and it was found that the increase in FA concentration plays the most critical role in membrane fouling. The increase in FA concentration led to an increase in the extracellular polymer (EPS), dissolved microorganism product (SMP) and soluble chemical oxygen demand (SCOD) concentration. FA was extremely significantly correlated with EPS and SCOD, and the FA concentration was approximately 20.7 mg/L. The SCODeff (effluent SCOD concentration) concentration was approximately 147 mg/L higher than the SCODinf (influent SCOD concentration) concentration. FA mainly affects membrane fouling by affecting the concentration of EPS and SCOD.

Evaluation of impact of sludge types and solids content on sludge treatment using microwave enhanced advanced oxidation process

ABSTRACT The microwave enhanced advanced oxidation process (MW-AOP) has been applied to pre-treat different sludge types and high solids content. Secondary sludge not only had the highest solids and nutrient content but also yielded higher treatment efficiency than primary or mixed sludge. In the case of secondary sludge with 4% total solids (TS), the total suspended solids (TSS) concentration was reduced by 32% while soluble chemical oxygen demand concentration increased from 1% to 40% after treatment at 110°C. A high level of nutrient release was also achieved; about 65% total phosphate (TP) solubilized at 110°C. The degree of secondary sludge disintegration was dictated by temperature and hydrogen peroxide dosage. The optimal operating temperature for the system was 110°C, and sludge containing TS up to 8% was treated effectively. Secondary sludge with 8% TS had a TSS reduction of 41% after treatment at 110°C while COD solubilization was about 45%; about 55% TP was solubilized at 10 min holding time. Treatment of sludge with higher solids content would allow for handling larger amounts of sludge at a given period and reduce heating cost per unit of treated sludge. The inter-relationship between the degree of sludge disintegration and changes in chemical and physical properties was also clearly demonstrated here. The treated sludge would be an ideal substrate for anaerobic digestion or phosphorous recovery processes. High levels of nutrients (phosphorus and nitrogen) and metal release, and solids disintegration from sludge containing high solids content would make subsequent resource recovery processes more effective and economical.

Long-term treatment of municipal wastewater using a mesh rotating biological reactor and changes in the biofilm community

The effects of temperature and hydraulic retention time on the sewage treatment performance of mesh rotating biological reactor (MRBR) were investigated. The MRBR contained net-like 3D plastic mesh disks instead of conventional rotating disks. A laboratory-scale MRBR was used to treat real sewage for over 1 year. The soluble chemical oxygen demand concentrations for the effluent were 48–64 mg/L whether the hydraulic retention time was 2 or 4 h and when the influent sewage temperatures was between 12.2 and 24.5 °C. The sewage temperature strongly affected the NH 4 + -N removal rete, which decreased by 0.1 kg N m − 3 day − 1 for each 12 °C decrease in temperature. Even though the NH 4 + -N removal rate was low, simultaneous nitrification and denitrification occurred at a removal efficiency of 95%. The microbial community structure in the biofilm attached to the MRBR disks was different to the microbial community structure of conventional activated sludge that had been used to treat the same sewage. The microbial community structure of the MRBR biofilm sludge was stable throughout winter and summer regardless of the hydraulic retention time. This suggested that the microbial community was initially controlled by the influent sewage but then became to specific to the MRBR. This was attributed to the high degree of simultaneous nitrification and denitrification that occurred. • Sewage treatment performance of a mesh rotating biological reactor (MRBR) evaluated. • BOD removal of a MRBR were 76%–90% during a year at HRT of 2 h. • High simultaneous nitrification and denitrification ratio was observed. • Microbial community of a MRBR biofilm was similar between in winter and summer. • MRBR biofilm have larger proportion of β - and γ -proteobacteria than activated sludge.

Alkaline pretreatment of tannery wastewater impact on biochemical methane potential tests: experimental study and kinetic modeling

Studies were carried out on anaerobic digestion of tannery wastewater obtained from leather processing. Degassed activated sludge biomass collected from a wastewater treatment plant was used as source of microorganisms. The study was carried out to examine the impact of alkaline pretreatment on a real tannery wastewater prior anaerobic digestion process. Bio-methane potential tests were conducted at 35±2°C on tannery wastewater pretreated by adding different volumes of 2N NaOH solution up to set pH values at 9, 10, 11, and 12, respectively. NaOH solution addition resulted in a partial removal of total Cr showing efficiency from 16.84 to 95.72% as well as in an increase of the soluble chemical oxygen demand concentration from 8.53 to 29.02%. The effects of this pretreatment affected significantly the results obtained with bio-methane potential tests that showed methane production from all the pretreated tannery wastewater samples much higher than from that unpretreated. Finally, the lag phase duration and the maximum specific methane production rate of the anaerobic digestion process were evaluated by fitting the experimental results from bio-methane potential tests with the following three models: (i) the modified Gompertz model, (ii) the Logistic function, and (iii) the Richards model. All the previous models showed a high level of accordance with the experimental data, even though Richards model resulted in being the most accurate.

Organic matter release from primary sludge by mechanical cutting

Surplus sludge disintegration to produce soluble organic matter for biological nutrient removal have been widely studied, however, the performance of mechanical disintegration of primary sludge is still unclear. A new mechanical cutting (MC) approach was proposed to disintegrate primary sludge in this study, the production and bioavailability of the soluble chemical oxygen demand (SCOD) was analyzed and the mechanism of organic matter release from primary sludge was investigated. With the mechanical cutting speed of 35,000 rpm, SCOD production increased with the increase of mechanical cutting time. When mechanical cutting for 8 min, the yield of organic matter reached the maximum, SCOD concentration and sludge disintegration degree (DD) were 1604 mg/L and 6.4 %, respectively. 32.3 % and 23.5 % of the SCOD was readily biodegradable organic matter (SS) and slowly biodegradable organic matter (XS). The denitrification rate of activated sludge was 2.23 mgNO3−-N/(gMLSS·h) with the organic matter released from primary sludge as carbon source, which was basically consistent with glucose. Mechanical cutting, centrifugation and pyrolysis were the main mechanisms for sludge disintegration and organic matter release, and pyrolysis played a major role.

Effect of Fe2+ and Fe0 Applied Photo‐Fenton Processes on Sludge Disintegration

AbstractThe disintegration of waste active sludge was investigated by photo‐Fenton processes. A batch study was conducted to evaluate parameters, such as Fe2+ and Fe0 ions and H2O2, governing the activated sludge integration by the photo‐Fenton process. Under optimum conditions, the concentration of soluble chemical oxygen demand (SCOD) with the classical Fenton process (CFP) increased very rapidly in the first five minutes due to the sufficient presence of reaction components in the medium, and then the rate of increase declined. In the modified Fenton process (FTP), the SCOD concentration increased more slowly as metallic iron powder must first be dissolved. The photo‐Fenton process proved to be a feasible and efficient process for the disintegration of waste sludge.

Does the combined free nitrous acid and electrochemical pretreatment increase methane productivity by provoking sludge solubilization and hydrolysis?

Free nitrous acid based pretreatments are novel and effective chemical strategies for enhancing waste activated sludge solubilization. In this study, the synergetic effects of the combined free nitrous acid and electrochemical pretreatment on sludge solubilization and subsequent methane productivity were evaluated. The results indicated that pretreatment with 10 V plus 14.17 mg N/L substantially enhanced sludge solubilization, with the highest soluble chemical oxygen demand concentration of 3296.7 mg/L, 25.6-time higher than that without pretreatment (128.9 mg/L). Due to the potential toxicity of NO2− and NO3− to microorganisms and its bioprocesses, the methane production of sludge pretreated by free nitrous acid was significantly deteriorated. The maximum methane yield (152.0 ± 9.6 mL/g-VSadded) was observed at 10 V pretreatment alone, only 1.7% higher than that of the control (149.4 ± 1.6 mL/g-VSadded). Combined pretreatment indeed enhances the sludge solubilization and hydrolysis, but does not always induce an improved anaerobic digestion efficiency.

Effect of metal oxide based TiO2 nanoparticles on anaerobic digestion process of lignocellulosic substrate

Lignocellulosic materials are recalcitrant to bioconversion, due to their rigid physiochemical structure. In this work, the effects of Fe2O3–TiO2 and NiO–TiO2 nanoparticles (NPs) and FeCl3 and NiCl2 salts, on the anaerobic digestion (AD) of wheat straw have been investigated. For this purpose, metal oxide-TiO2 NPs were synthesized and fully characterized. Results showed that addition of 0.252 mg of NiO–TiO2/g total solids (TS) to batch assays resulted in increase of soluble chemical oxygen demand (COD) and 67% increase in volatile fatty acids (VFAs) concentration compared to control tests during the first 4 days of experiments. These results indicate that hydrolysis and acidogenesis rates have been enhanced due to addition of NPs. No significant effects have been observed in soluble COD and VFAs concentrations compared to control experiments by adding salts to the batch assays. Addition of NPs or salts led to an increase in methane production rate during the first 4 days of experiments.

Exploring Submerged Forward Osmosis for Water Recovery and Pre-Concentration of Wastewater Before Anaerobic Digestion: A Pilot Scale Study.

Applying forward osmosis directly on raw municipal wastewater is of high interest for the simultaneous production of a high quality permeate for water reuse and pre-concentrating wastewater for anaerobic digestion. This pilot scale study investigates, for the first time, the feasibility of concentrating real raw municipal wastewater using a submerged plate and frame forward osmosis module (0.34 m2) to reach 70% water recovery. Membrane performance, fouling behavior, and effective concentration of wastewater compounds were examined. Two different draw solutions (NaCl and MgCl2), operating either with constant draw concentration or in batch with draw dilution over time, were evaluated. Impact of gas sparging on fouling and external concentration polarization was also assessed. Water fluxes up to 15 L m−2 h−1 were obtained with clean water and 35 g NaCl/L as feed and draw solution, respectively. When using real wastewater, submerged forward osmosis proved to be resilient to clogging, demonstrating its suitability for application on municipal or other complex wastewater; operating with 11.7 g NaCl/L constant draw solution, water and reverse salt fluxes up to 5.1 ± 1.0 L m−2 h−1 and 4.8 ± 2.6 g m−2 h−1 were observed, respectively. Positively, total and soluble chemical oxygen demand concentration factors of 2.47 ± 0.15 and 1.86 ± 0.08, respectively, were achieved, making wastewater more suitable for anaerobic treatment.

Impact of anaerobically digested biosolids characteristics and handling conditions on dewatering performance at multiple facilities.

Anaerobically digested biosolids (ABD) characteristics that affect dewatering were assessed at three water resource recovery facilities (WRRF) with different handling practices. Dewatering performance at the three sites corresponded to different levels ofsoluble chemical oxygen demand (COD), ammonia (NH4 -N), and mono- and divalent cation concentrationsin ADB. Capillary suction time (CST) and a modified centrifugal technique were used to determine optimum polymer doses and to assess the impact of handling conditions on dewatering performance. Both techniques indicated that polymer dosing between 15 and 20kg/dry tonne was optimal for all facilities and that biosolids mixing and pumping did not significantly impact dewaterability. The CST values of anaerobically digested biosolids decreased as temperature increased, but no significant difference was found for either temperature or location of dewatering facilities. Sludge viscosity and rheological properties that vary with temperature appeared to have influenced CST values. Modified centrifugal technique results indicated cake solids were not affected by polymer make-up water or ADB temperature when emulsion polymer was used. This study shows the value of laboratory testing of biosolids under controlled conditions to identify and correct potential problems in full-scale operations. PRACTITIONER POINTS: Capillary suction time and a modified centrifugal technique were used to assess the impact of different process-related and environmental factors on dewatering. Higher concentrations of soluble COD (potentiallyextracellular polymeric substances - EPS) and low calcium (Ca) in anaerobically digested biosolids align with reduced dewaterability. Cell disruption and break down of floc structures due to storage/mixing and pumping of biosolids did not appear to negatively impact dewatering. Modified centrifugal test results did not provide conclusive evidence of whether dewatering of anaerobically digested biosolids could be significantly impacted by temperature over the range 15-30°C, especially when emulsion polymer is used. This study shows the value of laboratory testing of biosolids under controlled conditions to identify potential problems in the full-scale operations.