COD Destruction Research Articles

Long-term evaluation of the effect of peracetic acid solution on anaerobic wastewater treatment: Process performance and microbial community structure

Peracetic acid (PAA) has been extensively used in poultry processing as an effective disinfectant. However, PAA-bearing poultry processing wastewater can lead to severe upsets of biological wastewater treatment processes. The objective of this study was to assess the long-term effect of PAA solution (PAA and hydrogen peroxide, H2O2) on the anaerobic treatment of poultry processing wastewater. Five reactors were operated for 177 d, semi-continuously fed with poultry processing wastewater and gradually increased levels of H2O2 or PAA solution, added either to the wastewater before feeding (indirect addition), or to the reactors immediately after feeding (direct addition). Indirect, well pre-decomposed H2O2 and PAA had limited effect on biogas production and COD destruction. Biogas production was completely inhibited with direct addition of H2O2 at 227 mg/L, but recovered in ca. 2 d. Direct addition of PAA solution at 500/100 mg/L PAA/H2O2 completely inhibited biogas production and required ca. 18 d incubation for recovery. Methanogenesis was more impacted than fermentation. Long-term H2O2 or PAA solution addition led to a relatively low shift in both bacterial and archaeal communities. The major methanogenic orders were Methanosarcinales and Methanomicrobiales. Direct PAA solution addition decreased both acetoclastic and hydrogenotrophic methanogenic activity; acetoclastic methanogenesis was affected the most.

Temperature Phased Anaerobic Digestion at the Intermediate Zone of 45 °C: Performances, Stability and Pathogen Deactivation

Temperature phased anaerobic digestion (TPAD) systems with conventional sequences (first stage of 55 ℃ and second stage of 35 ℃) have been widely studied. However, very limited studies were available on TPAD system with the first stage operated at the intermediate zone of 45 °C, mainly due to the notion that limited microbial activity occurs within this zone. The objective of this research was to evaluate the performance, stability and the capability of 45 °C TPAD in producing class A biosolids, in comparison to a conventional TPAD. Four combinations of TPAD systems were studied, 45 ℃ TPAD 2.5/10 (1st stage solids retention time (SRT) 2.5 days/2nd stage SRT 10 days), 45 ℃ TPAD 7.5/10, 55 ℃ TPAD 2.5/10 and 55 ℃ TPAD 7.5/10. Among all, 45 ℃ TPAD 7.5/10 was found to have the best performances, attributed to its high volatile solids (VS) destruction (58%), minimal acetate accumulation (127 mg/L), high methane yield (0.58 m3 CH4/kg VS removed), high COD destruction solid COD (sCOD; 74% and total COD (tCOD) 54%) and minimal free NH3 content (67.5 mg/L). As for stability, stable pH distribution, high alkalinity content and low VFA to alkalinity ratio, indicated a well-buffered system. Additionally, the system had also able to produce class A biosolids. Therefore, proved that TPAD system operated at the intermediate zone of 45 ℃ can perform better than the conventional TPAD, hence, highlighting its economic advantage.

Electrochemical advanced oxidation for treating ultrafiltration effluent of a landfill leachate system: Impacts of organics and inorganics and economic evaluation

We treated landfill leachate using electrochemical advanced oxidation processes (EAOPs) with a boron-doped diamond (BDD) anode. Before EAOPs, the leachate was first treated using biological treatment (anoxic–aerobic) and then ultrafiltration (hereafter referred as biopretreated UF landfill leachate). We explored impacts of organics and inorganics (nitrogen – and chloride – species) for various current densities (1–80 mA/cm2). We found that EAOPs enhanced biodegradability (BOD/COD ratio) significantly from < 0.03 to up to 0.78. COD destruction followed a pseudo-first order model, with the rate constant and electric energy per order ranging from 0.91 to 28.29 h−1 and 17.1 to 127.5 kWh m−3, respectively. The current efficiency (CE) was 100% for current density 1 mA/cm2 and CE decreased to 57.8% as the current density increased to 30 mA/cm2. The oxidation priority was in this order: COD > nitrogen – species > chloride – species. The evolution of nitrogen – and chloride – species and their oxidation mechanisms were also investigated. The impact of Fickian diffusion and electrical field driven charged ion transport (EFDCIT) on the total mass transport was examined using the Nernst-Planck equation. We found that the contribution of EFDCIT was similar to diffusion for current densities higher than 64 mA/cm2. Finally, we compared the costs for standalone EAOPs and EAOPs integrated with subsequent biological treatment for biopretreated UF landfill leachate and found that the lowest cost for the latter one that meets the effluent discharge criteria was only 0.76 USD/m3. Our study proved that EAOPs are technically and economically promising technology for leachate treatment.

Enhancing soluble phosphate concentration in sludge liquor by pressurised anaerobic digestion

Recovery of phosphate from wastewater is challenging, with one of the best opportunities being recovery from sludge anaerobic digestion liquor, as struvite. However, this is limited by the proportion of total phosphorous which is soluble, due to in-digester metal ion precipitation. High-pressure anaerobic digestion may enable enhanced phosphate solubility (and hence recovery potential), without the use of added acid, due to an increased liquid phase CO2 concentration. This was tested at 2, 4, and 6 bar absolute (bara) vs a 1 bara control reactor, fed with activated sludge. Increased pressure significantly (p = 0.0008), increased the fraction of phosphate that was soluble, ranging from 52% at 1 bara, to 75% at 6 bara. Model based analysis indicated that the main reason for increased solubility was pH depression (down to 6.4 at 6 bara), rather than changes in ion pairing (with carbonates) or increases in ionic activity. However, biological performance was adversely impacted, with a substantial loss in VS and COD destruction (on the order of 5%–10% absolute). No organic acid accumulation was observed. Bacterial and archaeal communities were significantly impacted (p∼0.0003–0.0005), with a shift to specific organisms, including Bacteroidales Rikenellaceae within the bacteria, and a Deep Sea Euryarchaeotal Group at 2 bara, and Methanocellaceae within the archaea at 4 and 6 bara. The work indicates that high-pressure operation is a technically viable option to improve phosphate recovery, and produce a high-methane biogas product, but that the loss of overall conversion needs to be further addressed, possibly through two-stage digestion.

Transition of municipal sludge anaerobic digestion from mesophilic to thermophilic and long-term performance evaluation

Strategies for the transition of municipal sludge anaerobic digestion from mesophilic to thermophilic were assessed and the long-term stability and performance of thermophilic digesters operated at a solids retention time of 30days were evaluated. Transition from 36°C to 53.3°C at a rate of 3°C/day resulted in fluctuation of the daily gas and volatile fatty acids (VFAs) production. Steady-state was reached within 35days from the onset of temperature increase. Transitions from either 36 or 53.3°C to 60°C resulted in relatively stable daily gas production, but VFAs remained at very high levels (in excess of 5000mg COD/L) and methane production was lower than that of the mesophilic reactor. It was concluded that in order to achieve high VS and COD destruction and methane production, the temperature of continuous-flow, suspended growth digesters fed with mixed municipal sludge should be kept below 60°C.

Wet air oxidation as a pretreatment option for selective biodegradability enhancement and biogas generation potential from complex effluent

This study looks at the possibility of wet air oxidation (WAO) based pretreatment of complex effluent to selectively enhance the biodegradability (without substantial COD destruction) and facilitate biogas generation potential. A lab-scale wet air oxidation reactor with biomethanated distillery wastewater (B-DWW) as a model complex effluent (COD 40,000mgL−1) was used to demonstrate the proof-of-concept. The studies were conducted using a designed set of experiments and reaction temperature (150–200°C), air pressure (6–12bar) and reaction time (15–120min) were the main process variables of concern for WAO process optimization. WAO pretreatment of B-DWW enhanced the biodegradability of the complex wastewater by the virtue of enhancing its biodegradability index (BI) from 0.2 to 0.88, which indicate favorable Biochemical Methane Potential (BMP) for biogas generation. The kinetics of COD destruction and BI enhancement has also been reported.

Microthrix parvicella and Gordona amarae in mesophilic and thermophilic anaerobic digestion systems

The scope of the study presented in this paper is to determine the fate of the filamentous bacteria Gordona amarae and Microthrix parvicella in anaerobic digestion operating under mesophilic and thermophilic conditions. In order to detect and quantify foaming bacteria in the anaerobic digesters, a fluorescent in situ hybridization (FISH) method was developed and applied. This paper presents the results of a laboratory‐scale study that involved the operation of four lab‐scale anaerobic digestion systems operating in the mesophilic (35 °C) and thermophilic (55 °C) temperature ranges at 20 days’ detention time. According to the FISH counts of G. amarae and M. parvicella, it appears that thermophilic conditions resulted in a higher destruction of both filamentous bacteria, averaging approximately 97% and 94% for the single thermophilic digester and the dual thermophilic/ mesophilic system, respectively. Within the context of this study, the overall performance of the four different anaerobic digestion systems was evaluated in terms of biogas production per mass of volatile solids destroyed, COD destruction, sludge dewaterability and foaming characteristics. The dual stage systems used in this study outperformed the single stage digesters.

Anaerobic biodegradability of Tween surfactants used as a carbon source for the microbial reductive dechlorination of hexachlorobenzene

Three structurally-related, nonionic, polysorbate surfactants (Tween 60, 61, and 65) were used as the sole carbon source to sustain the microbial, sequential reductive dechlorination of hexachlorobenzene (HCB) in a mixed, methanogenic culture derived from a contaminated estuarine sediment. The surfactants were partially degraded and fermented to methane with no measurable accumulation of volatile fatty acids, indicating that methanogenesis was rapid relative to the rates of hydrolysis and acidogenesis. Addition of the methanogenesis inhibitor 2-bromoethanesulfonic acid resulted in acetate accumulation without impact on the sequential dechlorination of HCB. An anaerobic biodegradability assay was performed and the following data were obtained for the Tween 60, 61, and 65, respectively: 53, 62, and 62% COD destruction; 35, 57, and 48% COD to methane conversion; and 38, 38, and 45% COD to acetate conversion. These data suggest that the hydrophobic moiety (stearate) of the surfactants was preferentially degraded, most likely through beta-oxidation, to acetate and ultimately to methane and carbon dioxide. Between 38 and 47% of the initial surfactant COD remained after 46 d incubation, which most likely corresponds to the hydrophilic polyoxyethylene moiety. An anaerobic biodegradation pathway of the Tween surfactants is proposed.

Kinetics of phenol oxidation in a trickle bed reactor over active carbon catalyst

AbstractThe wet air oxidation of phenol over a commercial active carbon catalyst was studied in a trickle bed reactor (TBR) in the temperature and oxygen partial pressure ranges of 120–160 °C and 0.1–0.2 MPa, respectively. The performance of the active carbon was compared in terms of phenol and COD destruction. The weight change of active carbon due to reaction was also measured. Finally, oxic phenol adsorption isotherms were assessed in batch conditions at 25, 125 and 160 °C. In order to use the conversion data obtained from the TBR for a kinetic study, special care was taken to check the kinetic control in the TBR experiments. Several kinetic models including power law or Langmuir–Hinshelwood expressions were considered to describe the catalytic oxidation of phenol over active carbon. The simple power law model with first order dependence on both phenol and oxygen concentration predicted satisfactorily the experimental data not only over the entire range of operating conditions studied, but also outside its validity range. Copyright © 2005 Society of Chemical Industry

Production of acetic acid from thermally treated sewage sludge in an upflow anaerobic reactor

This research project demonstrates the potential for converting the materials present in partially digested sewage sludge to acetic acid for environmental protection purposes, e.g. use in production of calcium magnesium acetate for road deciding salt or scrubbing sulfur dioxide from atmospheric emissions to prevent acid rain problems. Thermal treatment at 121°C for diluted sewage sludge (5:1) in 0.1 N Ca(OH) 2 proved to be successful for solubilizing the suspended volatile solids in the digested sewage sludge. The reduction of such solids reached 57% on a dry weight basis. The more soluble sewage sludge could then be treated in a flow-through, low hydraulic retention time, packed column anaerobic reactor to produce acetic acid. The laboratory pilot process first involved suppressing the methane producing bacteria using 0.0005 N bromo ethane sulfonic acid (BES), then feeding the 2.5-1 up-flow anaerobic reactor with thermally conditioned sludge broth in batch and then in continuous feed modes operated at hydraulic retention times of 24, 8 and 4 h. The effluent was monitored for acetic acid production, COD destruction, pH, alkalinity, ammonia, and total nitrogen. Electron scanning microscope photographs were taken to examine the attachment of the acid producing bacteria to the support media. The efficiency of the production of total volatile fatty acids (TVFA) from the treated sewage sludge was 80, 87 and 90% of the theoretical bioconversion possible based on the amount of COD reduced (40–62%). Acetic acid was the major volatile acid form produced.

Preliminary Conversion Mechanisms in Anaerobic Digestion of Biological Sludges

The purpose of this study is to evaluate digester performance and examine the preliminary conversion steps in the anaerobic digestion of biological sludges that contain intact viable cells. Activated sludge of totally biological origin is fed to laboratory-scale anaerobic digesters. Particulate protein accounts for more than 80% of the degradable COD in the digester effluents. Carbohydrate concentrations are substantial, and lipids, soluble COD, and volatile acids concentrations are very low. Experiments with lysed (i.e., autoclaved) biological sludge indicate that hydrolysis of particulate protein is the major, rate-limiting step in the digestion of biological solids. Results also suggest that percent COD destruction is independent of influent concentration, supporting the use of a first-order rate to describe hydrolysis. A previously presented kinetic model, which considers cell death/lysis and hydrolysis of particulate biomass, is applied to the data presented herein.

Treatment of Landfill Leachate; Management Options

Abstract Three management options for the treatment of leachate from landfilled domestic solid waste have been evaluated. Research results show that leachate can be treated effectively in aerobic systems, with high organic carbon and ammoniacal nitrogen removals of &amp;gt;90% and &amp;gt;85% respectively. Optimum SRT of about 10 days is required. Anaerobic treatment (UASB) with HRT's of between 1.0 and 4.0 days results in COD destruction of about 85% with high methane production (400-600 mg/g COD removed) and provides an intermediate effluent suitable for polishing to a high standard. Recirculation of leachate through the landfill by itself cannot provide a complete treatment, although significant reductions in volume and strength of leachate can be obtained.