High Chemical Oxygen Demand Concentration Research Articles

Influence of influent on anaerobic ammonium oxidation in an Expanded Granular Sludge Bed-Biological Aerated Filter integrated system

Shortcut nitrification-denitrification, anaerobic ammonium oxidation (ANAMMOX), and methanogenesis have been successfully coupled in an Expanded Granular Sludge Bed-Biological Aerated Filter (EGSB-BAF) integrated system. As fed different synthetic wastewater with chemical oxygen demand (COD) of 300–1200 mg·L−1 and NH4+-N of 30–120 mg·L−1 at the outer recycle ratio of 200%, the influence of influent on ANAMMOX in the integrated system was investigated in this paper. The experimental results showed that higher COD concentration caused an increase in denitrification and methanogenesis but a decrease in ANAMMOX; however, when an influent with the low concentration of COD was used, the opposite changes could be observed. Higher influent NH4+-N concentration favored ANAMMOX when the COD concentration of influent was fixed. Therefore, low COD =NH4+-N ratio would decrease competition for nitrite between ANAMMOX and denitrification, which was favorable for reducing the negative effect of organic COD on ANAMMOX. The good performance of the integrated system indicated that the bacterial community of denitrification, ANAMMOX, and methanogenesis could be dynamically maintained in the sludge of EGSB reactor for a certain range of influent.

The Relationships Between Sulphate Reduction and COD/VFA Utilisation Using Grass Cellulose as Carbon and Energy Sources

The release of mine effluents can have a damaging impact on receiving water bodies. Therefore, treatment of mine waters before discharge is imperative. A novel biological SO²⁻₄ removal technology has been developed whereby the degradation/fermentation products of grass cellulose, volatile fatty acids (VFA), function as the electron donors and SO²⁻₄ as the electron acceptor. The aim of the study presented here was to elucidate the interactions between the cellulose degradation rate, the chemical oxygen demand (COD), VFA production and its/utilisation rate as well as the sulphate reduction rate. To this end, two stirred batch reactors were operated: a test and a control reactor. The results showed that high COD and VFA concentrations were achieved after cellulose degradation, which resulted in a rapid decrease in the SO²⁻₄ concentration in the test reactor. The VFA results indicated that propionic and butyric acids were preferentially utilised, producing acetate. In the control reactor, the VFA and the COD production increased initially at the same rate, followed later by a decrease at a similar rate. These results suggest that the degradation products formed were utilised by the methanogenic bacteria to produce methane rather than by the sulphate-reducing bacteria, since the control reactor contained no sulphate (Visser 1995). Furthermore, these results showed a clear relationship between the COD/VFA production and the SO²⁻₄reduction in the test reactor and between the COD and VFA pattern in the control reactor.

Naval derusting wastewater containing high concentration of iron, treated in UV photo-Fenton-like oxidation

The UV photooxidation with Fe(III) and H 2O 2 was employed to treat a naval derusting wastewater, which contains the high COD (chemical oxygen demand) and various metal concentrations exceptionally with high concentrations of citric acid and iron. Because of its iron containment, the Fenton-like reaction automatically took place with the added amount of H 2O 2. The decomposition rate was found in a sequence of: UV/H 2O 2/Fe(III) > UV/H 2O 2 > Fe(II)/H 2O 2.TwoH 2O 2 injection methods, single and multiple points, were evaluated. The multiple-point H 2O 2 injection was more efficient to decompose the citric acid. The decomposition of the synthetic citric acid and the real derusting citric acid wastewater was also compared. The 93% COD reduction of the derusting wastewater was achieved using the UV/H 2O 2/Fe(III) treatment.

Biodegradation performance of an anaerobic hybrid reactor treating olive mill effluent under various organic loading rates

The primary objective of this study was to evaluate the performance of a 20 l lab scale anaerobic hybrid reactor (AHR) combining sludge blanket in the lower part and filter in the upper part under varying organic loading rates (OLRs) in order to study biodegradation of olive mill effluent (OME). For this purpose, some parameters, such as total phenols, effluent chemical oxygen demand (COD), suspended solids (SS), volatile fatty acids (VFAs), and pH in the influent and effluent, and removal efficiencies for those parameters (except pH) were continuously monitored throughout the experimental period of 477 days. Eleven different organic loadings between 0.45 and 32 kg COD m −3 day −1 were imposed by either varying influent COD or hydraulic retention time (HRT). The results demonstrated that the AHR reactor could tolerate high influent COD concentrations. Removal efficiencies for the studied pollution parameters were found to be as follows: COD, 50–94%; total phenol, 39–80%; color, 0–54%; and suspended solids, 19–87%. The levels of VFAs in the effluent, which was principally acetate, butyrate, iso-butyrate, and propionate, varied between 10 and 2005 mg l −1 depending upon OLRs. A COD removal efficiency of 90% could be achieved as long as OLR is kept at a level of less than 10 kg COD m −3 day −1. However, a secondary treatment unit for polishing purposes is necessary to comply with receiving media discharge standards.

Characterization of Landfill Leachates by Molecular Size Distribution, Biodegradability, and Inert Chemical Oxygen Demand

This work presents results from a detailed characterization of landfill leachates of different ages from a landfill in a major Brazilian city. This characterization consists of determining the molecular size distribution and the inert chemical oxygen demand (COD) and the biodegradability of both aerobic and anaerobic processes. Results show that leachate with a high COD concentration leachate has low biodegradability. A significant fraction of the COD is not characterized as protein, carbohydrate, or lipids, which reinforces the hypothesis that the remaining fraction was present in all leachate fractions (less than 1 kDa; between 1 and 10 kDa; between 10 and 100 kDa; and greater than 100 kDa) and is refractory. These results suggest that leachates with such characteristics require treatment systems that use physical-chemical processes as a pre- or post-treatment step to biological processes.

Effect of organic loading rate on the performance of an up-flow anaerobic sludge blanket reactor treating olive mill effluent

The primary objective of this study was to evaluate the effects of the organic loading rate on the performance of an up-flow anaerobic sludge blanket (UASB) reactor treating olive mill effluent (OME), based on the following indicators: (i) chemical oxygen demand (COD) removal efficiency; and (ii) effluent variability (phenol, suspended solids, volatile fatty acids, and pH stability). The UASB reactor was operated under different operational conditions (OLRs between 0.45 and 32 kg COD/m3·day) for 477 days. The results demonstrated that the UASB reactor could tolerate high influent COD concentrations. Removal efficiencies for the studied pollution parameters were found to be as follows: COD, 47∼92%; total phenol, 34∼75%; color, 6∼46%; suspended solids, 34∼76%. The levels of VFAs in the influent varied between 310 and 1,750 mg/L. Our measurements of the VFA levels indicated that some of the effluent COD could be attributed to VFAs (principally acetate, butyrate, iso-butyrate, and propionate) in the effluent, which occurred at levels between 345 and 2,420 mg/L. As the OLRs were increased, more VFAs were measured in the effluent. A COD removal efficiency of 90% could be achieved as long as OLR was kept at a level of less than 10 kg COD/m3·day. However, a secondary treatment unit for polishing purposes is necessary to comply with discharge standards.

A reliable free chemical demand () method.

A simple, but reliable mercury free method to analyse chemical oxygen demand is introduced. The method is based on international standard procedures but avoids the highly toxic mercury. In the procedure the oxidation temperature is brought down from 148 °C to 120 °C. At this temperature the chloride interference is reduced to a large extent, whereas the oxidation of most compounds is still complete. Chloride interference is further reduced by addition of silver ions and practically absent at a molar ratio Ag+/Cl- over 1.7. Compounds that are difficult to oxidise even at 148 °C or only in the presence of silver ions are investigated at 120 °C. A slight reduction in recovery of 20-35% is observed for compounds like acetic acid, ethanol or lauryl sulfate in the absence of chloride. In the presence of 3000 mg L-1 chloride only the reduction for acetic acid is more pronounced due to the low availability of silver ions. The other compounds studied showed no further decrease in recovery. The interference of bromide is about 50% less at 120 °C than at 148 °C. The interference of ammonium in the presence of chloride is not confirmed in this method. The recovery of the method at high chloride and low COD concentration, i.e., at 3000 mg Cl- L-1 and 25 mg COD L-1, is acceptable (122%) whereas at 2000 mg Cl- L-1 and 25 mg COD L-1 it is better (110%). Precision is good; Relative standard deviations are 5.6% respectively 2.6%. The results of 99 wastewater samples over a wide range of chloride concentrations are similar compared to analyses based on ISO 15705 (cuvette) or ISO 6060. With the addition of 20 mL silver sulfate-sulfuric acid solution, the chloride in samples up to 3000 mg L-1 chloride is largely precipitated. More volume silver sulfate-sulfuric acid solution or a higher concentration of silver sulfate increases the range of samples that can effectively be analysed. The believed favourable effect of addition of Cr3+ to samples has not been confirmed. In the Netherlands 95% of about 100 000 wastewater samples that are analysed for COD each year have chloride concentrations below 3000 mg L-1 and could be analysed without the use of mercury. This may save as much as 10 kg mercury per annum. It will however require the additional use of about 0.5 kg of silver.

Economic analysis for wet oxidation processes for the treatment of mixed refinery spent caustic

AbstractSodium hydroxide (caustic) continues to be one of the primary reagents used in refineries and petrochemical plants to extract hydrogen sulfide, mercaptans, and organic acids from hydrocarbon streams. A local refinery had accumulated ∼5000 m3 of spent caustics containing cresylic and naphthenic compounds. The chemical oxygen demand (COD) concentrations must be reduced to less than 1 g/L prior to discharge to biotreatment. A simple and safe treatment system for this high volume and high concentration of COD is desired. Bench‐scale treatment of spent caustic by the Fenton's reagent process had a total COD removal of greater than 95%, and the effluent COD was lower than 1 g/L. The process was operated at a temperature lower than 80°C and ambient pressure. The capital cost was thus lower than that of the wet air oxidation (WAO) process that normally operates at 200°C and 28 bars. The cost of exporting spent caustic to a full‐service company in USA was $1.21 per gallon that was competitive with treatment at the individual generation sites on a short‐term basis. © 2008 American Institute of Chemical Engineers Environ Prog, 2008

Applicability of high rate transpiration system for treatment of biologically treated distillery effluent

The biologically treated distillery effluent (BTDE) contains intense colour, high total dissolved solids (TDS), chemical oxygen demand (COD) and biochemical oxygen demand (BOD). These properties even after primary, secondary and tertiary treatments contain high concentrations of TDS, COD and BOD. The paper highlights the safe disposal and treatment of BTDE on land through High Rate Transpiration System (HRTS). HRTS is a zero discharge, low cost, high-tech method for improving the quality of BTDE for potential reuse. The experiments conducted at bench and pilot scale showed that HRTS having coconut husk as a bedding material could successfully treat the BTDE with a hydraulic load of 200 m3 ha(-1) day(-1) having BOD of 100 mg l(-1) and 500 m3 ha(-1) day(-1) having BOD of 500 mg l(-1) with average COD load of 0.686 and 2.88 ton ha(-1) day(-1) during the post and pre monsoon periods respectively. There was no significant increase in the organic carbon of the soil irrigated with BTDE. The concentrations of various pollutants analyzed in the leachate were within the prescribed limit for the drinking water sources. The colour removal was 99 to 100% and BOD and COD were possible to treat with optimum hydraulic loading of BTDE through HRTS planted with Dendrocalamus strictus.

A graphite-granule membrane-less tubular air-cathode microbial fuel cell for power generation under continuously operational conditions

An air-cathode microbial fuel cell (MFC) is an efficient and sustainable MFC configuration for recovering electrical energy from organic substances. In this paper, we developed a graphite-granule anode, tubular air-cathode MFC (GTMFC) capable of continuous electricity generation from glucose-based substrates. This GTMFC produced a maximum volumetric power of 50.2 W m −3 at current density of 216 A m −3 ( R EX = 22 Ω). Electrochemistry impedance spectroscopy (EIS) measurements demonstrated an overall internal resistance of 27 Ω, consisting of ohmic resistance of R ohm = 13.8 Ω (51.1%), a charge-transfer resistance of R c = 6.1 Ω (22.6%) and a diffusion resistance of R d = 7.2 Ω (26.3%). Power generation with respect to initial chemical oxygen demand (COD) concentration was described well by an exponential saturation model. Recirculation was to found to have a significant effect on electrochemical performance at low COD concentrations, while such effect was absent at high COD concentrations. This study suggests a feasible and simple method to reduce internal resistance and improve power generation of sustainable air-cathode MFCs.

Starvation is not a prerequisite for the formation of aerobic granules

Activated sludge with sludge volume index (SVI)(30) of 77 ml g(-1) and SVI(30) of 433 ml g(-1) was inoculated to start up reactors R1 and R2, respectively. In both R1 and R2, cycle time of 1 h and the influent chemical oxygen demand (COD) concentrations of 1,000 mg l(-1) were employed. Initial settling time of 2 min resulted in the loss of a substantial amount of biomass as wash-out and high effluent COD concentrations within the first week of operation. This implied that there was no starvation phase in each cycle of R1 and R2 during the first week of operation. However, aerobic granules with a size above 400 mum formed by day 7. Thus, it was concluded that starvation was not a prerequisite for the formation of aerobic granules. When cycle time was 1 h, the instability of aerobic granules was observed. When cycle time was prolonged to 1.5 h and granular sludge of 200 ml was used to start up reactor R3, the reactor R3 reached steady state within 1 week. SVI, size, and the morphology of granular sludge in R3 remained stable during the 47-day operation, which indicated that prolonged starvation time had positive effects on the stability of aerobic granules.

Effects of chitosan on growth of an aquatic plant ( Hydrilla verticillata) in polluted waters with different chemical oxygen demands

Effects of chitosan on a submersed plant, Hydrilla verticillata, were investigated. Results indicated that H. verricillata could prevent ultrastructure phytotoxicities and oxidativereaction from polluted water with high chemical oxygen demand (COD). Superoxide dismutase (SOD) activity and malondialdehyde (MDA) contents in H. verticillata treated with 0.1% chitosan in wastewater increased with high COD (980 mg/L) and decreased with low COD (63 mg/L), respectively. Ultrastructural analysis showed that the stroma and grana of chloroplast basically remained normal. However, plant cells from the control experiment (untreated with chitosan) were vacuolated and the cell interval increased. The relict of protoplast moved to the center, with cells tending to disjoint. Our findings indicate that wastewater with high COD concentration can cause a substantial damage to submersed plant, nevertheless, chitosan probably could alleviate the membrane lipid peroxidization and ultrastructure phytotoxicities, and protect plant cells from stress of high COD concentration polluted water.

Oxygen Uptake Rate Measurements For Evaluation of Ozonation of Municipal Wastewater

Ozonation has become more frequently used as oxidant to reduce chemical oxygen demand (COD) and toxic substances in wastewater originating from different industrial processes. An ozonation pilot plant followed by two parallel biological filters are used to investigate the possibility to reduce the high concentration of refractory COD in the effluent from a municipal wastewater treatment plant, partly loaded with biologically treated wastewater from a large pharmaceutical industry. COD measurements are used to evaluate the overall reduction of organic matter, oxygen uptake rate (OUR) and volatile fatty acids measurements are used for evaluation of the biodegradability of the remaining COD after ozonation. The impact of the ozone dose on the overall COD degradation and degradability of the remaining COD has been estimated. Biochemical oxygen demand (BOD) measurements confirm that parts of the COD are converted into biodegradable organic matter by ozonation. Biofilters following the ozonation plant secure that any degradable organic matter produced by ozonation is removed, which is confirmed from OUR-measurements.

Sustainable Approach for Leachate Treatment: Electricity Generation in Microbial Fuel Cell

Electricity generation from landfill leachate was examined by using both a dual-chamber microbial fuel cell (MFC) and a single chamber MFC. Experimental results showed that the maximum power density of 2060.19 mW/m3 in the dual-chamber MFC and that of 6817.4 mW/m3 in the single chamber MFC were obtained. It was recognized that the difference in internal resistance for two MFC systems was the main reason for resulting in the difference of power generation. Power generation as function of chemical oxygen demand (COD) in single chamber MFC showed a Monod-type relationship with P max of 5920.96 mW/m3 and Ks of 251.39 mg/L at an external resistance of 500 Ω. Cyclic voltammetry showed that electrons were directly transferred onto the anode by bacteria in biofilms, rather than self-produced mediators of bacteria in the solutions. At low COD concentration, electricity generation was limited by the anode due to kinetic limitation; while at high COD concentration, the cathode was shown to have more significant effects on the electricity generation than the anode. COD in leachate could be removed when it increases, mainly because oxygen diffused from the cathode was substantially reduced by aerobic or anoxic bacteria in the anode chamber, leading to the substrate loss. Removal of ammonium-nitrogen was not observed in the single chamber MFC. This novel technology provides an economical route for electricity energy recovery in leachate treatment.

Influence of Nitrate and COD on Phosphorus and Nitrogen Removals under Batch Methanogenic and Denitrifying Conditions

In this study the effects of chemical oxygen demand (COD)-to-NO3-N ratio on phosphorus and nitrogen removals were investigated through denitrification and methanogenesis in batch reactors seeded with granulated anaerobic sludge. For the COD-to-NO3-N ratios varying between 2 and 3.7 maximum denitrification was observed. The volatile fatty acid (VFA) production decreased to 120 from 2,000 mg/L for the COD-to-NO3-N ratios varying between 2 and 3.7 through methanogenesis. The methane percentages were between 45 and 60% for the reactors exhibiting COD-to-NO3-N ratios of 2 and 3.7 on days 4–6. After days 10–12, the methane gas production ceased while the daily N2 gas production reached a maximum level of 42 mL for the COD to NO3-N ratios of 2 and 3.75. NO3-N was used as the electron acceptor after methanogenesis had been completed. High and low COD concentrations such as 10,000 and 200 mg/L decreased the PO4-P uptake, resulting in 10% PO4-P removal efficiency. COD concentrations of 2,000 and 4,000 mg/L increased the PO4-P uptake, resulting in PO4-P removal efficiencies of 89 and 95, respectively, in anoxic batch reactors. The NO3-N concentrations decreased to 500 from 1,500 mg/L at COD concentrations varying between 2,000 and 4,000 mg/L through PO4-P uptake under anoxic conditions. Suitable COD-to-NO3-N ratios provide effective NO3-N, PO4-P removals and minimize the external carbon requirement through anaerobic/anoxic treatment of nutrient containing wastewaters.

Simultaneous phosphorus, nitrogen and dinitrotoluene removals in batch anaerobic/anoxic/aerobic sequentials

The PO 4-P concentration increased to 320 mg/l through the simultaneous chemical oxygen demand (COD), volatile fatty acid (VFA) consumption and dinitrotoluene (DNT) removal resulting in phosphorus release under anaerobic conditions. When the COD to NO 3-N ratio was reduced to about 2.0, the organic fraction of wastewater was mainly converted to methane under NO 3-N containing anoxic conditions. Both denitrification and PO 4-P concentration began to increase when the methanogenesis has been completed, resulting in high N 2 gas productions. Through anoxic operation the Poly-P bacteria are capable of removing PO 4-P using VFA, COD as carbon source and NO 3-N as the electron acceptor after the denitrification process was mainly completed. With the influent COD of 3000 mg/l a total of the maximum removable PO 4-P was 56 mg/l through 20 days of anoxic incubation, indicating 98% P removal in this reactor at PO 4-P taken up /NO 3-N consumed and PO 4-P taken up /COD consumed ratios of 2.3–3.6 and 0.08–0.2. High NO 3-N concentrations decreased P uptake significantly. Very low and very high COD concentrations such as 500 and 7000 mg/l cause a significant reduction of phosphorus uptake under anoxic conditions. DNT was degraded to NH 4-N, aromatic amines and toluene through anaerobic condition while the aromatic amines, toluene and ammonia were ultimately mineralized under aerobic conditions throughout the sequential anaerobic/aerobic process. The 70% DNT removal efficiency were observed in anaerobic reactors while 37 and 0.05% DNT removal was obtained in anoxic P releasing and anoxic P taking-up conditions, respectively. No significant DNT removals (20%) was obtained through aerobic incubation while 50% DNT removal efficiency was obtained in sequential denitrification/P releasing anoxic conditions.