Higher Soluble Chemical Oxygen Demand Research Articles

Briefing: H2O2 dosing strategy on microwave treatment of sewage sludge

A H2O2 dosing strategy for microwave enhanced advanced oxidation process treatment of sewage sludge was formulated. The timing of hydrogen peroxide introduction in a continuous-flow 915-MHz system affected the treatment efficiency in terms of solids destruction, nutrient release and volatile fatty acid (VFA) production. Introducing hydrogen peroxide into the treatment set at 60°C was found to be more effective than adding it at the beginning. The treatment set with hydrogen peroxide introduced at 60°C resulted in higher soluble chemical oxygen demand concentrations and VFAs, higher soluble total Kjeldahl nitrogen and soluble total phosphate and also improved dewaterability and settling. However, there were no differences in terms of ammonia and orthophosphate release between the two treatment schemes. It is an advantage to introduce hydrogen peroxide into the treatment set at 60°C in a continuous-flow microwave system.

Effect of temperature on short chain fatty acids (SCFAs) accumulation and microbiological transformation in sludge alkaline fermentation with Ca(OH)2 adjustment

The effects of temperatures (15–55 °C) on the alkaline fermentation of sewage sludge were investigated in semi-continuous stirred tank reactors (semi – CSTR) at the pH of 10. The highest soluble chemical oxygen demand (SCOD) yield was obtained at 55 °C (764.2 mg/(gVS L d)), while the highest short chain fatty acids (SCFAs) yield was observed at 35 °C (319.8 mg/(gVS L d)), 1.5 times higher than SCFAs yield at 55 °C (209.5 mg/(gVS L d)). The proportion of the intercellular organic substances being transferred to the slime layer of sludge flocs increased from 29% at 15 °C to 54% at 55 °C. But only a small part of soluble organic substances in the slime layers was converted to SCFAs at 55 °C. The dewaterability of sludge was better at 35 °C than that at 55 °C. Microbiological community analysis showed the acid-producing microorganisms at the medium temperatures (25 °C and 35 °C) were more diverse and abundant than those at the low (15 °C) and high temperatures (55 °C). Clodtridium and Bacillus in Firmicutes and Gamma proteobacterium in Proteobacteria were the dominant functional bacterial species for high SCFA accumulation.

Energy-efficient stirred-tank photobioreactors for simultaneous carbon capture and municipal wastewater treatment.

Algal based wastewater treatment (WWT) technologies are attracting renewed attention because they couple energy-efficient sustainable treatment with carbon capture, and reduce the carbon footprint of the process. A low-cost energy-efficient mixed microalgal culture-based pilot WWT system, coupled with carbon dioxide (CO2) sequestration, was investigated. The 21 L stirred-tank photobioreactors (STPBR) used light-emitting diodes as the light source, resulting in substantially reduced operational costs. The STPBR were operated at average optimal light intensity of 582.7 μmol.s(-1).m(-2), treating synthetic municipal wastewater containing approximately 250, 90 and 10 mg.L(-1) of soluble chemical oxygen demand (SCOD), ammonium (NH4-N), and phosphate, respectively. The STPBR were maintained for 64 days without oxygen supplementation, but had a supply of CO2 (25 mL.min(-1), 25% v/v in N2). Relatively high SCOD removal efficiency (>70%) was achieved in all STPBR. Low operational cost was achieved by eliminating the need for mechanical aeration, with microalgal photosynthesis providing all oxygenation. The STPBR achieved an energy saving of up to 95%, compared to the conventional AS system. This study demonstrates that microalgal photobioreactors can provide effective WWT and carbon capture, simultaneously, in a system with potential for scaling-up to municipal WWT plants.

Simulation modelling of dissolved organic matter removal in a free water surface constructed wetland

A simulation model was developed to explain the reduction of dissolved organic matter (DOM) in a free water surface constructed wetland (FWS-CW). Laboratory-scale experiments were conducted in the FWS-CW system of the water reclamation plant of Hat Yai municipality in Southern Thailand. The FWS system was divided into different layers of FWS-CW components according to their mechanisms and the kinetic coefficient (k). The DOM, in terms of the soluble chemical oxygen demand (SCOD) concentrations simulated by the calibrated model, exhibited moderate agreement with the full-scale data. The model showed that the leaching of SCOD from the gravel bed is the most significant mechanism affecting the SCOD concentration in the wetland ponds. Although the organic loading rate (OLR) of the SCOD inflow of the FWS-CW was low, a high SCOD concentration in these ponds was still observed under the conditions of a long hydraulic retention time (HRT) and a slow hydraulic loading rate (HLR). Hence, FWS-CW management should focus on the relationship between HLR and HRT, as well as sludge management in the system, to prevent the release of SCOD. When this model was stimulated with the operational data of the FWS-CW under study, it revealed that the HRT should not exceed 2 days to prevent high SCOD discharge into the water reservoir.

A comparative study of ultrasonication, Fenton's oxidation and ferro-sonication treatment for degradation of carbamazepine from wastewater and toxicity test by Yeast Estrogen Screen (YES) assay

A comparative study of ultrasonication (US), Fenton's oxidation (FO) and ferro-sonication (FS) (combination of ultrasonication and Fenton's oxidation) advanced oxidation processes (AOPs) for degradation of carbamazepine (CBZ) from wastewater (WW) is reported for the first time. CBZ is a worldwide used antiepileptic drug, found as a persistent emerging contaminant in many wastewater treatment plants (WWTPs) effluents and other aquatic environments. The oxidation treatments of WW caused an effective removal of the drug. Among the various US, FO and FS pre-treatments carried out, higher soluble chemical oxygen demand (SCOD) and soluble organic carbon (SOC) increment (63 to 86% and 21 to 34%, respectively) was observed during FO pre-treatment process, resulting in higher removal of CBZ (84 to 100%) from WW. Furthermore, analysis of by-products formed during US, FO and FS pre-treatment in WW was carried out by using laser diode thermal desorption-atmospheric pressure chemical ionization (LDTD-APCI) coupled to tandem mass spectrometry (MS/MS). LDTD-APCI–MS/MS analysis indicated formation of two by-products, such as epoxycarbamazepine and hydroxycarbamazepine due to the reaction of hydroxyl radicals (OH) with CBZ during the three types of pre-treatment processes. In addition, the estrogenic activity of US, FO and FS pre-treated sample with CBZ and its by-products was carried out by Yeast Estrogen Screen (YES) assay method. Based upon the YES test results, none of the pre-treated samples showed estrogenic activity.

The Effects of Microwave Pretreatment of Dairy Manure on Methane Production

This study was undertaken to evaluate the efficiency of a liquid-solids separation process and microwave pretreatment, as well as anaerobic biodegradability of microwave pretreated dairy manure. Liquid-solids separation of raw dairy manure resulted in solid and liquid fractions having different properties, with the solid fractions richer in total and volatile solids content and liquid fractions richer in nutrients and metal ions. Substantial amounts of soluble chemical oxygen demand and nutrients were released into the solution after the microwave treatment. The microwave pretreated dairy manure was also subjected to anaerobic digestion. The kinetic parameters of methane production potential, maximum methane production rate and lag time were determined using the modified Gompertz equation. Anaerobic digestion of liquid manure, without microwave treatment, outperformed the sets with microwave treatment. The microwave-treated liquid dairy manure, without acid addition had better results in terms of methane potential and methane production, than with acid addition. Thermophilic digestion exhibited a higher maximum methane production rate than that of mesophilic digestion, but lower methane yields. The microwave pretreatment of dairy manure resulted in high soluble chemical oxygen demand; however, methane yield was not increased.

Enzymatic Hydrolysis of FoodWaste and Methane Production Using UASB Bioreactor

Complex carbohydrates of food waste (FW) can be converted to biogas, methane. In this article, enzymatic solubilization of FW and methane production potential using an upflow anaerobic sludge blanket (UASB) reactor of FW liquor enzymatically hydrolyzed were investigated. The optimum conditions of FW hydrolysis were enzyme mixture ratio of 1:2:1 with carbohydrase: protease: lipase, respectively, 0.2% (w/w FW) of mixture dose, and 10-h hydrolysis reaction. More than 95% of high soluble chemical oxygen demand (SCOD) removal efficiency and 0.35 L-CH4/g-SCOD of high methane yield were observed at 9.1 g-SCOD/L/d of organic loading rate. Our results revealed that methane production via a UASB reactor in conjunction with enzymatic hydrolysis of FW could be a novel anaerobic digestion process to obtain high-value biogas.

Freezing as a combined wastewater sludge pretreatment and conditioning method

Laboratory experiments were carried out to investigate the potential of freezing as a combined sludge pretreatment and conditioning method, which could not only improve wastewater sludge dewaterability but also solubilize sludge solids. The effect of freezing temperature, freeze thaw cycles on solubilization of organic matter, release of nutrients, dewaterability and particle size distribution was examined. The treatment efficiency of the freezing technique was compared with thermal and combined thermal chemical (acidification or basification) pretreatment methods. The efficacy of the combined chemical and freezing treatment was also tested for the first time. Experimental results indicated that freezing was effective in the solublization of sludge solids. About 2- to 8-fold increase in soluble chemical oxygen demand (SCOD), 2–8 times in ammonia (NH 3–N) and 1.5–2.5 times in orthophosphate (OPO4–P) concentrations were observed after freezing treatment. Sludge samples with combined basification and freezing treatments had the higher SCOD and NH 3–N concentrations while acidifying prior to freezing did not enhance treatment efficiency. Freezing significantly improved sludge dewaterability. Freezing caused the aggregation of small particles and greatly increased the volume of large particles. Freezing has a potential as a combined sludge pretreatment and conditioning method that could provide more befits than as only a sludge conditioning technique.

Effect of ultrasonic and alkaline pretreatment on sludge degradation and electricity generation by microbial fuel cell

Both ultrasonic and alkaline pretreatment of excess sewage sludge were investigated to enhance organic degradation and electricity generation from sludge by the subsequent microbial fuel cell (MFC). The ultrasonic pretreatment showed that the degree of sludge disintegration was directly related to the energy input, ultrasonic density and duration. Alkaline pretreatment demonstrated that more soluble organic matters were released from the sludge with more NaOH dose and longer reaction time, and the degree of sludge disintegration within 30 min accounted for 45-76% of that for 24 h. When ultrasonic and alkaline pretreatment were combined, the released chemical oxygen demand (COD) was higher than those with ultrasonic or alkaline pretreatment alone. Ultrasonic and alkaline (pH=11) pretreatment could enhance electricity generation from sludge by the subsequent MFC, resulting in more degradation of total COD (TCOD) and volatile solids (VS). Slight change in power output from the MFC was observed due to the higher soluble chemical oxygen demand (SCOD) in the pretreated sludge. By using the combined ultrasonic and alkaline pretreatment of sludge, the removal efficiencies of TCOD and VS were increased from 27.1% to 61.0% and 35.2% to 62.9% in comparison with raw sludge, respectively, and the power output in MFC was slightly increased from 10.3 W/m(3) to 12.5 W/m(3).

Enhanced solubilization and anaerobic biodegradability of source-separated kitchen waste by microwave pre-treatment

Results from an investigation of the effect of high temperature and pressure microwave (MW) pre-treatment of source-separated kitchen waste (SSKW) are presented. MW pre-treatment to a temperature of 175 °C (1 min holding time) at a heating rate of 7.9 °C min(-1), enhanced SSKW solubilization by 40% in comparison with control; yielding higher soluble chemical oxygen demand (sCOD), total sugars and proteins concentrations in the soluble phase (<45 μm). Batch biochemical methane potential tests (BMP) at 33 °C, indicated an enhanced anaerobic biodegradability compared to non-pretreated samples. However, the comparative analysis of semi-continuous anaerobic digesters performance for pre-treated and non-treated SSKW, indicated that MW pre-treatment was successful at solids retention times (SRT) higher than 25 days, showing not only a robust performance in terms of volatile solids (VS) and total chemical oxygen demand (TCOD) removals (6 and 5% gain, respectively, in comparison with control). Effluent dewaterability was also enhanced by MW pre-treatment, showing a 20% increase for the best operation conditions. The study of biomass activity revealed the production of difficult to degrade compounds during pre-treatment conditions and also served as a tool to monitor reactor performance deterioration.

Effect of microwave irradiation on anaerobic degradability of model kitchen waste

High temperature and pressure microwave (MW) irradiation was investigated as a pre-treatment to enhance anaerobic biodegradability and methane production from a model kitchen waste (KW). Heating rates of 7.8, 3.9 and 1.9 °C/min from room temperature to a final pre-treatment temperature of 175 °C with 1 min temperature holding time were tested. MW irradiation was successful in solubilization of particulate chemical oxygen demand (COD) resulting in higher soluble COD, protein and sugar concentrations in the supernatant phase (<0.45 μm) as well as in the whole fraction of pretreated KW compared to controls (not pretreated). Anaerobic biodegradability of the supernatant and whole fractions of pretreated KW was assessed by using a batch biochemical methane potential assay (BMP) at 33 °C. Although the highest level of solubilization was achieved at a heating rate of 1.9 °C/min, improvement in anaerobic biodegradability was observed only at the fastest heating rate of 7.8 °C/min for whole waste and for all conditions with the supernatant phase. BMP indicated increased biodegradability of between 5% and 16% for the supernatant fraction relative to controls. For the whole fraction, anaerobic biodegradability improved by 9% at a heating rate of 7.8 °C/min.

Evolution of composition of dairy manure supernatant in a controlled dung pit

Anaerobic conversion of dairy manure into biogas is an attractive way of managing this waste. It is well known that the hydrolysis of large molecules into small, directly biodegradable ones is the rate limiting step of the overall anaerobic process. The present work studies the development of the hydrolytic and acidogenic stages of dairy manure with different solid concentrations (40, 60 and 80 g VS/L) at ambient temperature (20 °C). The purpose was to determine the operational conditions that provide a liquid fraction with a high soluble chemical oxygen demand (COD) and a high volatile fatty acids (VFA) content in manure before the methanogenic stage starts up. At 20 °C, the evolution of the studied parameters showed that, in a controlled plug‐flow dung pit, the hydrolytic and acidogenic stages progressed moderately in a continuous way during the 25 days that the experimentation lasted, whereas no methanization was observed. Supernatant COD and VFA concentrations increased 30% and 107%, respectively, for the 60 g VS/L samples. Manure was also operated at 35 °C with a similar increase in supernatant COD but a higher increase in VFA, 154%. For both operational temperatures, the predominant VFAs were, in this order, acetic, propionic and butyric acids. During the operation at 35 °C, the methanogenic stage started between days 20 and 25 for the samples with lower solids content, i.e. 40 and 60 g VS/L.

Effects of anaerobic pre-treatment on the degradation of dewatered-sewage sludge

Effects of anaerobic pre-treatment were evaluated on the dewatered-sewage sludge from a municipal wastewater treatment plant in order to improve its biodegradability through anaerobic digestion. The pre-treatment was conducted in laboratory scale at 25, 50 and 70 °C for an incubation time of two days. As a reference, sludge sample was also autoclaved at 121 °C for 20 min to determine the thermal effect to the subsequent sludge digestion. Characteristics of dewatered-sludge such as viscosity, pH and soluble chemical oxygen demand (SCOD) were affected by the pre-treatment. A higher SCOD after the pre-treatment did not necessarily imply an increase in methane yield, although initial biodegradability rate was improved. In fact, a ‘great’ improvement in SCOD concentration (up to 27%) was translated in only 8% increase in the methane yield (298 ± 9 and 276 ± 6 Nml CH 4 gVS added −1 for pre-treated and untreated samples, respectively). Increasing the anaerobic pre-treatment time from 12 h to 2 days at 50 °C led to an 11% improvement in methane yield. Methane content in biogas increased from an average of 65–69% for the pre-treated and untreated substrates, respectively. Volatile solids (VS) reduction increased from 42% to 51%. The overall digestion time was not affected by the pre-treatment but 90% of methane was produced in the first 12 days of incubation for 50 °C pre-treated samples whereas it took 2–5 days more for 25, 70 °C pre-treated and untreated sludge samples. In this study, thermophilic digestion was also found to be a better option in terms of faster digestion and higher VS-reduction, but it showed lower methane yield as compared to mesophilic digestion, i.e. 9% and 11% increment in methane yields for thermophilic and mesophilic digestions, respectively.

Influence of anaerobic co-digestion of sewage and brewery sludges on biogas production and sludge quality

This research investigated operating parameters and treatment efficiency for the digestion of sewage and brewery sludge. The prime objective of this study was to enhance the quality of treated sludge for use as agriculture fertilizer and to enhance biogas production, a by-product that can be used as an energy source. Three bench-scale completely stirred tank reactor (CSTR) anaerobic digesters were operated at mesophilic condition (36 ± 0.2°C). A mixture of sewage and brewery sludge were used as substrates at ratios of 100:0, 75:25, 50:50, 25:75 and 0:100, based on wet weight basis (w/w). For each digester, the solids retention times (SRT) were 20 days. The organic loading and volatile solids loading were between 1.3–2.2 kg chemical oxygen demand (COD)/m3/day and 0.9–1.5 kg/m3/day, respectively. The digester fed with brewery sludge as co-substrate yielded higher treatment efficiency than sewage sludge alone. The removal efficiencies measured in terms of soluble chemical oxygen demand (SCOD) and total chemical oxygen demands (TCOD) ranged from 40% to 75% and 22% to 35%, respectively. Higher SCOD and TCOD removal efficiencies were obtained when higher fractions of brewery sludge was added to the substrate mixture. Removal efficiency was lowest for sewage sludge alone. Measured volatile solid (VS) reduction ranged from 15% to 20%. Adding a higher fraction of brewery sludge to the mixture increased the VS reduction percentage. The biogas production and methane yield also increased with increase in brewery sludge addition to the digester mixture. The methane content present in biogas of each digester exceeded 70% indicating the system was functioning as an anaerobic process. Likewise the ratio of brewery sewage influenced not only the treatment efficiency but also improved quality of treated sludge by lowering number of pathogen (less than 2 MPN/g of dried sludge) and maintaining a high nutrient concentration of nitrogen (N) 3.2–4.2%, phosphorus (P) 1.9–3.2% and potassium (K) 0.95–0.96%. The heavy metals, chromium (Cr) and copper (Cu) remaining in digested sludge were present at relatively high levels (Cr 1,849–4,230 and Cu 930–2,526 mg/kg dried sludge). The metals were present as organic matter-bound and sulfide-bound fractions that are not soluble and available. The digested sludge could be safely applied to soil as a plant nutrient source, without fecal coliforms or heavy metals risk. A sludge mixture ratio of 25:75 (sewage:brewery), which generated the higher nutrient concentrations (N = 4.22%, P = 3.20% and K = 0.95%), biogas production and treatment efficiency meet the Bangkok Metropolitan Administration (BMA) safety guidelines required for agricultural application. Biogas production and methane at the 25:75 ratio (sewage:brewery) yielded highest amount of VSremoved (0.65 m3/kg) and CODremoved (220 L/kg), respectively.

Landfill leachate treatment by MBR: Performance and molecular weight distribution of organic contaminant

A membrane bioreactor (MBR) with an air-lift bioreactor and gravity flow is applied to treating landfill leachate. More than 99% of BOD5 (biochemical oxygen demand for five days) removal efficiency is achieved with less than 35 mg/L of BOD5 in the effluent at less than 1.71 kg BOD5/m3·d of BOD5 loading rate. When DO (dissolved oxygen) is maintained at the range of 2.3–2.8 mg/L and the loading rate of NH4 +-N (ammonium nitrogen) is kept at 0.16–0.24 kg NH4 +-N/m3·d, the NH4 +-N in the effluent is less than 15 mg/L. However, compared with high removal rates of BOD5 and NH4 +-N, the removal efficiency of soluble chemical oxygen demand (SCOD) varies between 70% and 96%. The investigation of molecular weight (MW) distribution has been carried out by the gel permeation chromatography (GPC) so as to understand the fate of organic matters in the MBR treating of landfill leachate. Results indicate that organic matters of the landfill leachate are composed of a high MW fraction (MW of the peak, MW p = 11480–13182 Da) and a low MW fraction (MW p = 158–275 Da). The high MW fraction is not biodegradable, but can be decreased with microfiltration membrane. The most of the low MW fraction is biodegradable, but the residue of the low MW fraction is able to permeate through the membrane, thus resulting in high SCOD in the effluent of the MBR.

The effect of residual chemical oxygen demand on anoxic and aerobic phosphate uptake and release with various intracellular polymer levels.

This study investigated the anoxic and aerobic phosphate uptake and release reactions and the fraction of denitrifying phosphate-accumulating organisms (DPAOs) under various initial chemical oxygen demand (COD) and residual COD conditions. The results showed that DPAOs and non-DPAOs could release phosphate when high soluble COD was present. Consequently, the phosphate-uptake potential was dynamic and increased when the initial COD increased, the initial polyhydroxyalkanoates (PHA) increased, and the residual COD decreased. Furthermore, the electron acceptor (oxygen of nitrate) has more significant influence on the phosphate uptake/release characteristics, while the residual COD concentrations have little influence on that. The fraction of DPAOs to phosphate-accumulating organisms was 42% when the initial PHA storage was enough by both DPAOs and non-DPAOs. This was closely related to the relative phosphate uptake (47%) in the anoxic zone of the process.