Total Chemical Oxygen Demand Reduction Research Articles

Performance and microbial community composition of full-scale high-rate cascade sludge digestion system via pie-shaped reactor configuration

A full-scale high-rate cascade anaerobic digestion (CAD) system was evaluated for its ability to enhance enzymatic sludge hydrolysis. The system included a newly built digester, innovatively divided into three pie-shaped compartments (500 m3 each), followed by an existing, larger digester (1500 m3). The system treated a mixture of waste activated sludge and primary sludge, achieving a stable total chemical oxygen demand reduction efficiency (56.1 ± 6.8 %), and enhanced sludge hydrolytic enzyme activities at a 14.5-day total solids retention time (SRT). High-throughput sequencing data revealed a consistent microbial community across reactors, dominated by consortia that govern hydrolysis and acidogenesis. Despite relatively short SRTs in the initial reactors of the CAD system, acetoclastic methanogens belonging to Methanosaeta became the most abundant archaea. ‬‬‬‬‬‬‬‬‬‬‬‬‬ This study proves that the CAD system achieves stable sludge reduction, accelerates enzymatic hydrolysis at full-scale, and paves the way for its industrialization in municipal waste sewage sludge treatment.

Understanding of the potential role of carbon dots in promoting interspecies electron transfer process in anaerobic co-digestion under magnetic field: Focusing on methane and hydrogen production

Anaerobic digestion shows great potential for biomass energy recovery, however, the low electron transfer efficiency between microorganisms limits overall anaerobic digestion performance. In this work, aloe peel-derived carbon dots (carbon quantum dots, CQDs) were designed and investigated as accelerants for anaerobic digestion systems under an applied magnetic field to promote the interspecific electron transfer (IET) efficiency in methane and hydrogen production processes. Compared with the control group (188.9 mL/g VS, 4.2 mL/g VS, 34.7 %, and 26.3 %), the applied magnetic field (5 mT) significantly increased methane yield (256.1 mL/g VS), hydrogen yield (7.0 mL/g VS), total chemical oxygen demand reduction (41.7 %), and energy conversion efficiency (35.7 %). The introduction of the CQDs (0.18–0.45 wt.%) under a magnetic field (5 mT) has further positive effects on digestion performance. The experimental group incorporating 0.36 wt.% CQDs under a 5 mT magnetic field obtained the highest methane yield (348.9 mL/g VS), hydrogen yield (9.9 mL/g VS), and total chemical oxygen demand reduction (58.4 %), and thus the energy recovery efficiency was increased by 85 % compared with control group. The digestate incorporating 0.36 wt.% CQDs exhibited excellent thermal stability (59.71 %) and total nutrient content (38.17 g/kg), and has great potential as a main ingredient in compound fertilizer. The potential role of the magnetic field and CQDs in enhancing hydrogen interspecies electron transfer (HIET) and direct interspecies electron transfer (DIET) for methane and hydrogen production is further illustrated, providing a feasible solution for improving energy recovery from biomass.

Anaerobic co-digestion of agro-industrial wastes using anaerobic sequencing batch reactor for bio-energy recovery: Focus on process performance and stability of the methanogenic step

Anaerobic co-digestion of tannery wastewater (TWW) with dairy wastewater (DWW) using a two-phase anaerobic sequencing batch reactor (ASBR) was evaluated. For this purpose, laboratory-scale anaerobic digesters, one for acidogenesis and the other for methanogenesis, with 0.4 and 0.6 L of working volume, respectively, operated in semi-continuous mode, were used. The results showed that a methanogenic reactor treating the effluent acidogenic reactor (50 % TWW and 50 % DWW) exhibits the best process performances in terms of daily biogas (64.7 mL/day), methane production (461 mL/day), specific methane yield (892 mL CH4/g COD), methane content (71.2 %), and total chemical oxygen demand (TCOD) removal efficiency (85.6 %) when operated at a hydraulic retention time (HRT) of 15 days. This indicated that the addition of DWW improves the anaerobic co-digestion process, increasing biogas production (64.7 mL/day) by about 41 % as compared with anaerobic co-digestion of 100 % TWW (27.4 mL/day). The process stability of the methanogenic stage of the two-stage anaerobic digestion process was also evaluated, and the obtained result showed suitable pH (6.70), no total volatile fatty acid (TVFA) accumulation (VFA/alkalinity: 0.363), alkalinity (3350 mg CaCO3/L), and ammonia (231 mg/L) within the optimum operating range. Furthermore, high overall performance efficiency in terms of TCOD reduction (88.8 %) in the two-phase (acidogenesis and methanogenesis) anaerobic digester of 50:50 (TWW:DWW) was obtained when operated at a HRT of 18 days (3 days for acidogenesis and 15 days for methanogenesis). Anaerobic co-digestion of TWW with DWW generally resulted in increased process stabilities and performances compared to mono-digestion of TWW.

An integrated hydrodynamic-biokinetic model to optimize the treatment processes in a laboratory-scale, pilot-scale, and full-scale bioreactor

One major disadvantage of membrane bioreactors (MBRs) is the high operating and aeration costs, and optimizing the process to attain economic efficiency is essential. In this study, a hydrodynamic - biokinetic integrated model was developed by combining a multiphase computational fluid dynamics (CFD) model with a population balance (PBM) submodel, an activated sludge (ASM1) submodel, and a combined (EPS – SMP) CES submodel. The developed integrated model was used to investigate the efficiency of treatment of bioreactors on three different scales (case 1- laboratory, case 2 – pilot, and case 3- full-scale system). The simulated values of bubble size count, total chemical oxygen demand (TCOD), total nitrogen (TN), ammonical nitrogen (SNH), nitrate‑nitrogen (SNO), EPS, and SMP concentrations were well validated with the experimental results, with an error percentage of 2.8 %, 6.32 %, 2.25 %, 0.53 %, 1.19 %, 4.62 %, and 2.05 %, respectively. The validated model is then extended for sensitivity analysis to identify optimum conditions (H/B ratio, H/S ratio, and bubble size) to reduce TCOD and TN concentration. The maximum percentage reduction in TCOD and TN concentrations in the most optimum scenario was 20 and 23 %, respectively, for case 3. Also, a reduction of 32 % in the cost of aeration was observed (for case 3) when the bubble size was reduced to 5 mm (from the current value of 7 mm). The preceding results suggest that the integrated model successfully optimized the treatment processes.

Biofilm characterization in removal of total chemical oxygen demand and nitrate from wastewater using draft tube spouted bed reactor.

The present paper investigates the effect of dilution rate on the removal of total chemical oxygen demand and nitrate in the draft tube spouted bed reactor and morphological characteristics of biofilms formed by microorganisms ofmixed culture on granular activated carbon (GAC). The nitrate and total chemical oxygen demand (COD) decreased from 97 to 81% and 95% to 87% respectively with increase in dilution rate from 0.6/hto 1.5/hshowing that residence time in the reactor governs the nitrate and total COD reduction efficiency. Lower dilution rates favor higher production of biomass and extracellular polymeric substances (EPS). It was observed that the nitrate and total COD reduction rate increased with time along with simultaneous increase in EPS production. Thus, the performance of a reactor in terms of dynamic and steady-state biofilm characteristics associated with nitrate and organic reduction is a strong function of dilution rate. Hence these findings indicate that a draft tube spouted bed reactor is capable of simultaneously reducing total organics and nitrogen in industrial/municipal wastewater, as this reactor possesses two distinct regions aerobic and anoxic conditions which can prevail in different parts of a reactor.

Macronutrient solubilisation during hydrothermal treatment of sewage sludge

A first step in assessing the potential of the hydrothermally treated sludge as a fermentation medium or as fertiliser, among other more innovative uses, is to study in depth the compositional changes that take place during the hydrothermal treatment of secondary sewage sludge. Thus, the present study analyses, for the first time, the effects of the reaction time, temperature, pressure and atmosphere on the properties of the hydrolysates obtained and, in particular, on the fate of the four main macronutrients (C, N, P and K). Under the most aggressive operational conditions tested (200 °C, 50 bar, 210 min and oxidising atmosphere), 76% of total suspended solids were disintegrated and 94%, 96%, 12% and 41% of C, N, P, and K were solubilised, with the majority of these changes occurring during the first 60 min of treatment. Nevertheless, these conditions also resulted in significant mineralisation of the organic carbon (77% total Chemical Oxygen Demand reduction) and the formation of notable concentrations of ammonium (around 64 g/kg dry matter) and small amounts of nitrates and nitrites (0.14 g/kg dry matter). After long reaction times, the re-alkalinisation of the reaction medium favoured the binding of soluble P to dissolved metal ions and its subsequent precipitation. Temperature and type of atmosphere did not significantly influence the soluble K concentration, suggesting that this element mainly interacts with tightly bound extracellular polymeric substances in the raw sludge. Finally, pressure did not have significant effects on the final macronutrient composition of the treated sludge.

Co-Digestion of Household Black Water with Kitchen Waste for a Sustainable Decentralized Waste Management: Biochemical Methane Potential and Mixing Ratios Effects

The generation of anthropogenic wastes, such as household human feces and kitchen waste, has resulted in a severe environmental impact. Sustainable management approaches to address disposal challenges and harness potential nutrient and energy values are urgently needed. This investigation assessed the anaerobic co-digestion of food waste and black water to identify the biochemical methane potential. The household kitchen waste showed improved performance at a dilution ratio of 50% with biochemical methane potential of 265 mL CH4/g volatile solid (VS), and that of the black water was 220 mL CH4/g VS without dilution. This trend indicates their easy biodegradation/digestibility and potential for energy recovery. The kitchen waste equal mix ratio of 50% v/v with the black water had the highest biochemical methane potential of 295.13 mL CH4/g VS when co-digested. High performance was due to the comparative balance in substrate concentrations that offered robust methanogenic activities without inhibitions. The effluent total chemical oxygen demand reduction of ∼90% and other physicochemical parameters showed that the codigestion treatment (kitchen waste and black water 50:50% v/v) was efficient. The codigestion route could offer a decentralized wastewater management system for energy recovery.

Application of halophiles in air cathode MFC for seafood industrial wastewater treatment and energy production under high saline condition

Abstract The present study details the application of potential halophiles obtained from desalination plant for treatment of seafood wastewater and energy production under high saline condition (8%). Air cathode microbial fuel cell (ACMFC) reactor was employed to study the wastewater treatment efficacy of halophiles under high saline condition. Research investigation was performed at different organic load (OL) 0.5, 1, 1.25 and 1.5 gCOD/L under high saline condition. Initial TCOD (Total Chemical Oxygen Demand) removal efficiency at 0.5 gCOD/L was 58 ± 1.2%% with 340 mW/m2 power density by the halophiles in ACMFC. Increment in OL to 1 and 1.25 gCOD/L recorded 85 ± 2.1% and 90 ± 2% TCOD removal with corresponding power density of 550 and 570 mW/m2 in ACMFC operated under saline condition. Further increase in the OL to 1.5 gCOD/L revealed decrease in the TCOD reduction and energy production. The maximum electricity of 980 mV with power density of 570 mW/m2 and 600 mA/m 2 current density was generated at 1.25 gCOD/L. Columbic efficiency was 52% at 0.5 gCOD/L and declined to 33% and 23% at 1 and 1.25 gCOD/L OL concentration. A maximum TSS removal of 78 ± 1.5% was attained at 1.25 gCOD/L OL in ACMFC. The study revealed 1.25 gCOD/L as the optimized OL for potential treatment of seafood industrial wastewater and energy production. Bacterial community analysis performed with samples from anode and sludge region disclosed the presence of dynamic halophilic strains such as Ochrobactrum (MT118968), Marinobacter (MT118969), Martelella (MT118970), Rhodococcus (MT118971), Bacillus (MT118972), Stenotrophomonas (MT118973), Alicyclobacillus (MT118974), Microbacterium (MT118975), Xanthobacter (MT118976), Pseudomonas (MT118977) and Sedimentibacter (MT118978). Predominance of Ochrobactrum, Marinobacter, Martelella, Rhodococcus and Bacillus depicted at 1.25 gCOD/L in the anode and sludge samples from ACMFC.

Enhancement of overloaded waste stabilization ponds using different pretreatment technologies: a comparative study from Namibia

Abstract Waste stabilization ponds (WSP) are a well-established wastewater treatment technology in Namibia. However, they are often overloaded and we still lack concepts and technologies for improvement. Therefore, this study presents the full-scale implementation of two pretreatment technologies to reduce the inflow of organic and solid loads into a facultative pond. We specifically compared the effects of anaerobic biological and mechanical pretreatment by an upstream anaerobic sludge blanket (UASB) reactor and a 250 μm micro sieve (MS). Not only in Namibia but also in most sub-Saharan countries, there is little experience with these technologies for the treatment of municipal wastewater in small and fast-growing local communities. Both technologies were tested in parallel for a period of 17 months and proved operational. While the UASB achieved better removal results with respect to chemical oxygen demand (COD) and suspended solids (TSS), the MS was more flexible in handling changing inflow patterns and had a much smaller footprint. The average total COD reductions of the MS and the UASB were 22 and 50%, respectively. TSS were removed by 45% with the MS and by 57% with the UASB reactor. Therefore, UASB and MS are viable options for the enhancement of existing WSP to reach better effluent values of the facultative pond.

Mesophilic anaerobic co-digestion of acorn slag waste with dairy manure in a batch digester: Focusing on mixing ratios and bio-based carbon accelerants

Co-digestion of acorn slag waste (ASW) and dairy manure (DM) with two bio-based carbon (BC) accelerants are investigated via batch experiments under mesophilic condition. With the favorable synergistic effect of the mixed substrate and BC accelerant, the anaerobic digestion (AD) systems assembled with aloe peel-derived BC (2.16 g/L) show significantly improved methanogenesis on the basis of the optimum wet weight ratio of ASW to DM (1:3). The cumulative biogas yield is 580.9 mL/g VS, and the total chemical oxygen demand reduction is 79.37%. These results are higher than those of the AD systems without carbon-based accelerants. The feasibility of digestate utilization is evaluated by thermal and fertilizer analyses, which manifest outstanding stability and excellent fertility (6.93%−7.40%) of digestate in co-digestion systems. A general strategy for understanding the enhanced methanogenesis pathways, induced by BC in AD systems, is demonstrated. These important findings open an innovative opportunity for developing carbon-based accelerants in anaerobic co-digestion.

Cost effective sludge reduction using synergetic effect of dark fenton and disperser treatment

The proposed work intended to improve sludge reduction efficiency of dark Fenton (DF) treatment. Dark Fenton reduces 61% of sludge in 90 min under the optimized Fe (II) and H2O2 dosage of 0.008 g/g suspended solids (SS) and 0.032 g/g SS respectively at pH 3. Combination of dark Fenton with disperser (DFD) reduces time required for the treatment from 90 to 30 min with the disperser specific energy input of 835.536 kJ/kg total solids (TS). At 30 min reaction time, mixed liquor suspended solids and total chemical oxygen demand reduction were found to be 65% and 60%, respectively for DFD. The efficiency of DFD treatment revealed best fit with R2 value of 0.989 during pseudo first order kinetic analysis. The synergistic effect of DFD resulted in 29% higher MLSS reduction and 31% higher TCOD reduction than dark Fenton (DF) in 30 min treatment as the obtained MLSS and TCOD reduction at 30 min treatment time was observed to be 65% and 60% in DFD and 36% and 29% in DF, respectively. Although, DFD demands higher energy input (233.69 kWh), it had potency to reduce higher solids concentration in a short duration and this results in a net profit of 12.852 USD/ton of sludge.

Effect of aerobic pretreatment on anaerobic digestion of olive mill wastewater (OMWW): An ecoefficient treatment

Anaerobic digestion experiments of olive mill wastewater (OMWW) without pretreatment were carried out and signs of inhibition in the biological process were observed after a time equal to 1.5 times the Hydraulic Residence Time (HRT) due to the presence of a high inhibitors concentration in OMWW. Based on these findings, OMWW was subjected to an aerobic pretreatment in order to reduce the concentration of phenolic compounds and decrease Total Chemical Oxygen Demand (TCOD), achieving a reduction of 78% and 90% of the initial polyphenols concentration and 18% and 21% TCOD reduction when the substrate was aerated for 5 and 7 days respectively.Finally, anaerobic digestion experiments using OMWW aerated for 5 and 7 days as substrate were conducted to determine the influence of aeration time on methane yields and TCOD reduction. The results yield 5 days as the aeration time that achieves best results, given that this stabilizes the anaerobic process, can reduce the TCOD by 65% and generates almost 0.39m3 methane/kg removed TCOD.Anaerobic digestion of OMWW will be economically feasible if the waste is pretreated by aerobic digestion, since the period of return of investment obtained under these conditions does not exceed 6 years.

Disintegration of waste activated sludge by different applications of Fenton process

Oxidative disintegration of municipal waste activated sludge (WAS) using conventional Fenton (Fe2++H2O2, CFP) and Fenton type (Fe0+H2O2, FTP) processes was investigated and compared in terms of the efficiency of sludge disintegration and enhancement of anaerobic biodegradability. The influences of different operational variables namely sludge pH, initial concentration of Fe2+ or Fe0, and H2O2 were studied in detail. The optimum conditions have been found as catalyst iron dosage=4g/kg TS, H2O2 dosage=40g/kg TS and pH=3 within 1h oxidation period for both CFP and FTP. Kinetics studies were performed under optimal conditions. It was determined that the sludge disintegration was happened in two stages by both processes: rapid and subsequent slow disintegration stages and rapid sludge disintegration stage can be described by a zero-order kinetic model. The effects of oxidative sludge disintegration under the optimum conditions on anaerobic digestion were experienced with biochemical methane potential (BMP) assay in batch anaerobic reactors. Total methane production in the CFP and FTP pre-treated reactors increased by 26.9% and 38.0%, relative to the untreated reactor (digested the raw WAS). Furthermore, the total chemical oxygen demand reductions in the pre-treated reactors were improved as well.

The start-up and saline adaptation of mesophilic anaerobic sequencing batch reactor treating sludge from recirculating aquaculture systems

Treatment of sludge from aquaculture is a matter of special importance and there is a need for salt-tolerant biological wastewater treatment to coincide with the development of brackish/marine aquaculture. The aims of the current study were to determine the ability of anaerobic sequencing batch reactor (ASBR) to anaerobically digest sludge from fresh-water recirculating aquaculture systems and the ability of adaptation to low saline conditions. The mesophilic ASBR were evaluated with loading rates between 0.12 and 0.41g chemical oxygen demand (COD)/day at a 20-day hydraulic retention time (HRT) for start-up and with organic loading rates (OLR) of 0.39–0.41gCOD/Lday at a 20-day HRT for saline adaptation. The average removal rate of total chemical oxygen demand (TCOD), total suspended solids (TSS) and volatile suspended solids (VSS) of the ASBR were above 97%, 96% and 91% during the stabilization period of the experimental reactors. The average daily gas production of ASBR was between 0.013 and 0.022L/g TCOD from day 118. A sludge-mass reduction of up to 94±2.3%, TCOD reduction of 44±13% and VSS/SS of 39–70% were demonstrated for the reactor performance during the gas production period. However, the process of gas production was obviously inhibited, presumably by salt, and unstable due to the dissolved COD (DCOD), total ammonium nitrogen (TAN) and alkalinity of the effluents of the experimental reactors and TSS and sludge volume index (SVI) observed within the reactors. The daily gas production was observed to decrease during the saline adaptation period and stopped when the salinity of the effluents was higher than 8.7ppt until the end of the experiment.

Sono-thermal pre-treatment of waste activated sludge before anaerobic digestion

Sonication and thermalization can be applied successfully to disrupt the complex waste activated sludge (WAS) floc structure and to release extra and intra cellular polymeric substances into soluble phase along with solubilization of particulate organic matters, before sludge digestion. In this study, sonication has been combined with thermalization to improve its disintegration efficiency. It was aimed that rise in temperature occurring during the sonication of sludge was used to be as an advantage for the following thermalization in the combined pre-treatment. Thus, the effects of sonication, thermalization and sono-thermalization on physical and chemical properties of sludge were investigated separately under different pre-treatment conditions. The disintegration efficiencies of these methods were in the following descending order: sono-thermalization>sonication>thermalization. The optimum operating conditions for sono-thermalization were determined as the combination of 1-min sonication at 1.0W/mL and thermalization at 80°C for 1h. The influences of sludge pre-treatment on biodegradability of WAS were experienced with biochemical methane potential assay in batch anaerobic reactors. Relative to the control reactor, total methane production in the sono-thermalized reactor increased by 13.6% and it was more than the sum of relative increases achieved in the sonicated and thermalized reactors. Besides, the volatile solids and total chemical oxygen demand reductions in the sono-thermalized reactor were enhanced as well. However, it was determined that sludge pre-treatment techniques applied in this study was not feasible due to their high energy requirements.

Treatment of fruit-juice industry wastewater in a two-stage anaerobic hybrid (AH) reactor system followed by a sequencing batch reactor (SBR)

This study has been carried out to assess the performance of a combined system consisting of an anaerobic hybrid (AH) reactor followed by a sequencing batch reactor (SBR) for treatment of fruit-juice industry wastewater at a temperature of 26 °C. Three experimental runs were conducted in this investigation. In the first experiment, a single-stage AH reactor was operated at a hydraulic retention time (HRT) of 10.2 h and organic loading rate (OLR) of 11.8 kg COD m−3 d−1. The reactor achieved a removal efficiency of 42% for chemical oxygen demand (COD), 50.8% for biochemical oxygen demand (BOD5), 50.3% for volatile fatty acids (VFA) and 56.4% for total suspended solids (TSS). In the second experiment, two AH reactors connected in series achieved a higher removal efficiency for COD (67.4%), BOD5 (77%), and TSS (71.5%) at a total HRT of 20 h and an OLR of 5.9 kg COD m−3 d−1. For removal of the remaining portions of COD, BOD5 and TSS from the effluent of the two-stage AH system, a sequencing batch reactor (SBR) was investigated as a post-treatment unit. The reactor achieved a substantial reduction in total COD, resulting in an average effluent concentration of 50 mg L−1 at an HRT of 11 h and OLR of 5.3 kg COD m−3 d−1. Almost complete removal of total BOD5 and oil and grease was achieved, i.e. 10 mg L−1 and 1.2 mg L−1, respectively, remained in the final effluent of the SBR.

Development of a modified three-stage methane production process using food wastes.

A modified three-stage system was developed for the rapid production of methane from food wastes. The primary stage was a semianaerobic hydrolysis/acidogenic system, in which approx 4100 mg/L of volatile fatty acids (VFAs) was produced at a hydraulic retention time (HRT) of 2 d. The operation temperature and pH were 30 degrees C and 5.0-5.5, respectively. The non-degraded materials were removed through a hole at the bottom of the reactor. The secondary stage was an anaerobic acidogenic system equipped with an upflow anaerobic sludge blanket (UASB) type of fermentor. VFA was accumulated up to 6100 mg/L by the addition of Clostridium butyricum to the reactor at an HRT of 2 d. The optimum temperature and pH range were 35 degrees C and 5.0-5.5, respectively. The tertiary methanogenic stage produced CH4 and CO2 from the VFA in the UASB reactor. Methane content was 72% of the total gas volume, and the yield was 0.45-0.50 m3/kg of volatile solids at an HRT of 12 d. The operation temperature and pH were 41 degrees C and 7.6-7.9, respectively. The three-stage process exhibited an unusually high total chemical oxygen demand reduction rate up to 95%. Total nitrogen decreased to 96% and < 10 mg/L of total phosphorus remained in the final effluent.