Influent Soluble Chemical Oxygen Demand Research Articles

Simultaneous Nitrification and Denitrification of Municipal Wastewater in Aerobic Membrane Bioreactors

Simultaneous nitrification-denitrification (SND) of municipal wastewater was investigated in a laboratory-scale membrane bioreactor (MBR) operated at two different hydraulic retention times (HRTs), 0.5 and 1 day, dissolved oxygen 3.0 to 0.5 mg/L, and solids retention time (SRT) between 28 and 120 days. The organic loading rate (OLR) (0.11 to 0.64 kg chemical oxygen demand [COD]/m3/d) and influent soluble COD (SCOD)/ total Kjeldahl nitrogen (TKN) ratio (5 to 19) were varied by the addition of glucose. The ammonia-nitrogen and TKN removals were over 97%, and total nitrogen removal was approximately 89% in the MBR. The maximum specific nitrification rates (98 mg N/d/g VSS) and specific denitrification rates (81 mg N/d/g VSS) occurred at an SCOD/TKN ratio of 9.1. The optimum conditions for maximum total nitrogen removal by SND in a single reactor MBR have been found to be low dissolved oxygen (< 0.6 mg/L) and high OLR (approximately 0.64 kg COD/m3/d) at an HRT of 0.5 day and SRT of approximately 85 days.

Uptake of Wastewater Organic Matter to Activated Sludge

The influences of contact time and ratio of food to microorganism (F/M) on uptake of wastewater organic matter in a short contact process were investigated using three activated sludge batch reactors fed with synthetic wastewater, sewage and livestock wastewater. About 64% of influent soluble chemical oxygen demand (SCOD) in the synthetic wastewater and 61% of SCOD in the sewage and 43% of SCOD in the diluted livestock wastewater were adsorbed into the activated sludge within 30 min. The specific mass of organic matter uptaken in the synthetic wastewater was 55 mg SCOD/g mixed liquor suspended solids (MLSS). In the same manner, 20 and 14 mg SCOD/g MLSS were calculated as the values in the sewage and livestock wastewater, respectively.

Development of an empirical model for domestic wastewater treatment by biological aerated filter

An empirical model for wastewater treatment by biological aerated filters (BAF) was developed in the study, which relates influent soluble chemical oxygen demand (sCOD) to effluent sCOD and medium bed height in order to simply engineering design and verify experimentally the suitability of this model and ascertain the relationship between the constant values calculated with the model and reactor performance. The theoretical model was based on design of contact oxidation process and conventional biofilter because these fixed-film processes show similar flow pattern. Firstly, the two parallel BAF systems packed with lava medium and expanded clay medium, respectively, were run for actual domestic wastewater at different hydraulic loading rates during the experiment. A great deal of data was then used to the empirical model, which was based on a first-order reaction, to calculate the empirical values of n (medium constant) and K (overall process constant). The experimental results show that the treatment efficiency of lava medium exceed to that of expanded clay medium, which just conform to what the model predict, the higher value of K the greater efficiency of sCOD removal, and the lower value of n the greater variation of sCOD removal indicating a poor resistance to shock loading. Next, the effect of suspended solid (SS) on model was estimated by simulated domestic wastewater to verify its feasibility.

Treatment of fish-processing wastewater by co-culture of Candida rugopelliculosa and Brachionus plicatilis

This research was conducted as a part of the continuous development of a novel technique for managing fish-processing wastewater by cultivating proteolytic yeast, Candida rugopelliculosa, as possible diet of the rotifer, Brachionus plicatilis. It was feasible to use Alaska Pollack processing wastewater as a growth medium for C. rugopelliculosa, which was stimulatory for growth of the rotifer by 18.3% over the commercial diet of Saccharomyces cerevisiae. Maximum growth of C. rugopelliculosa and reduction of influent soluble chemical oxygen demand (SCOD) concentration were respectively (6.09±0.04)×10 6 cells/ml and 70.0% at 6.3 h hydraulic retention time (HRT). Method of 4th order Runge–Kutta approximation was successfully applied to determine the Monod kinetics of C. rugopelliculosa by using unsteady state data from only one continuous unsteady state operation at a fixed HRT. The maximum microbial growth rates, μ max, and half saturation coefficient, K s, were determined to be 0.82±0.22 h −1 and 690±220 mg SCOD/L, respectively. The microbial yield coefficient, Y, and microbial decay rate coefficient, k d, were determined to be (1.39±0.22)×10 4 cells/mg SCOD and 0.06±0.01 h −1, respectively.

Fermentation of a low VFA wastewater in an activated primary tank

A low volatile fatty acid wastewater from a Barcelona residential area was prefermented in a laboratory-scale primary clarifier operated as a prefermenter -an activated primary tank. Total suspended solids (TSS), oxidation-reduction potential (ORP) and temperature were measured in the prefermenter. Influent and effluent were characterised through chemical oxygen demand (COD), soluble COD, volatile fatty acids (VFA), VFA potential, soluble PO4-P, NH4-N, pH and alkalinity. Solids retention times (SRT) of 5 d and 10 d were tested. Best results were obtained for the 5 d SRT with the prefermenter covered for better temperature and ORP control. For these conditions, COD solubilisation was measured as 22 mg COD/l, 66 mg COD/g influent particulate COD, or 91 mg COD/g influent VSS. VFA-formation was measured as 34 mg VFA-COD/l, 142 mg VFA-COD/g influent VSS, or 77 mg VFA-COD/g influent COD. These values indicate remarkable solubilisation and fermentation in the prefermenter. The VFA/PO4-P ratio was improved from 0.9 to 5.5 mg VFA-COD/mg PO4-P, but did not approach the recommended value for biological P removal (20 mg/mg). VFA production could not reach the influent VFA-potential either (110 mg VFA-COD/l) and VFA-potential was lower in effluent than in influent. With a 5 d SRT and the prefermenter uncovered, a small VFA formation and no solubilisation were observed. This was interpreted as the VFA being formed from the influent soluble COD. With a 10 d SRT, a very low ORP was measured. Neither solubilisation nor VFA production were detected in the prefermenter. Concurrent acidogenic fermentation and methanogenesis are compatible with these results. P and N solubilisation was low or moderate in the prefermenter over all periods, and increased with increasing SRT and TSS, and decreasing ORP, and pH and alkalinity were quite stable, due to the high influent alkalinity and the moderate VFA formation and N solubilisation. WaterSA Vol.28(1) 2002: 89-98

Organic and nitrogen removal with minimal COD requirement by integration of sequestered denitrification and separate nitrification in a low-loaded activated sludge process

A separate sludge system incorporating sequencing batch reactor (SBR) for sequestered denitrification and an immobilized fixed-film reactor for nitrification was investigated in this study. Emphases were placed on the preservation of organic matter as an electron donor for denitrification and the improvement of nitrification efficiency by using an immobilization technique with alginate coating. To preserve organic materials in the sludge required for denitrification, a study was made with a contact process. The contactor, when operated with a short detention time, gave incomplete metabolism of organic matter. With 64% of the influent soluble chemical oxygen demand (SCOD) was adsorbed to activated sludge within 30 min. The specific mass of organic matter uptaken was 55 mg SCOD/g mixed liquor suspended solids (MLSS), which enhanced the denitrification efficiency up to 63% in the following denitrification step. Thus, the required COD in the proposed system can be saved up to 63% as an available electron donor for the conventional aerobic process. The immobilized nitrification unit showed over 90% of nitrate production rate up to 50 mg/l of influent ammonia load.

The optimum substrate to biomass ratio to reduce net biomass yields and inert compounds in biological leachate treatment under pure-oxygen conditions

To investigate the effect of both initially present soluble inert COD (SI) and soluble inert COD formed by microbial activities (SPM) on the effluent soluble residual COD (SR) and to determine biokinetic constants, the pure-oxygen was employed for the batch assays of biological leachate treatment. The results of this work showed that the effluent residual soluble COD was entirely composed of SI and SPM, therefore, could not be reduced below 7–10% of total influent soluble COD (ST0.inf), corresponding to the organics removal efficiency of 93–90%. The value of SI of leachate, which is associated with the types of wastewaters, was determined as approximately 7.84% of ST0.inf, and the soluble inert COD by microbial activities was assessed by means of the coefficient fPM of 0.0474. These results mean that significant amount of feed leachate COD may pass the biological system without any change. On the basis of the concept that microorganisms must satisfy their maintenance energy requirements prior to synthesizing new biomass, a set of batch assays with various ratios of ST0.inf /X0 were carried out to evaluate their effects on the excess biomass production. Decreasing the supply of substrate per unit biomass resulted in gradual decrease in the biomass yields, but, at the same time, it resulted in gradual increase in the bacteria mediated inert COD as a side effect. The optimum ratios of ST0.inf /X0 were concluded as 0.2–0.6 according to the careful consideration of both aspects on the reduction of net sludge yields and inert COD from microbial activities.

Biological uptake of influent organic matter as an electron donor for denitrification by activated sludge

To preserve organic materials in the sludge required for denitrification, a study was made with a contact process. The contactor, when operated with a short retention time (30 min), gave incomplete metabolism of organic matter. With 64% of the influent soluble COD (SCOD) was adsorbed to activated sludge within 30 min. The specific mass of organic matter uptaken was 55 mg SCOD/g Mixed Liquor Suspended Solids that enhanced the denitrification efficiency up to 63% in the following denitrification step.

Modelling biological aerated filters for wastewater treatment

Biological aerated filters (BAFs) are submerged three-phase fixed-media reactors for wastewater treatment. A major characteristic of BAF reactors is the use of granular media which allows solids separation as well as secondary or tertiary biological treatment in one unit. The aim of this work was to design a simple empirical model relating influent soluble chemical oxygen demand (sCOD) to effluent sCOD and reactor height, verify experimentally the suitability of this model and ascertain the relationship between model constants and reactor performance. The theoretical model was based on that designed for trickling filters as both fixed-film processes show a similar plug flow pattern. Two reactors were set up to run parallel treating settled domestic sewage using media identical in size and shape, except one was less dense than water (relative density 0.92) and the other was denser than water (relative density 1.05). The reactors were run upflow with liquid flowrates of 0.29–0.58 m 3 d −1 (0.2–0.5 litres min −1) and an air:liquid ratio of 10:1. After 4 weeks from start-up, steady-state was reached. From this point, samples were taken at different heights along the reactors at timed intervals and profiles of sCOD removal against reactor height were produced. This analysis was repeated for a number of different flowrates and organic loadings (0.57–1.40 kg sCOD m −3 d −1). The resulting data was then used with the empirical model, which was based on a first-order reaction, to calculate the values of k∗ (overall process constant) and n (media factor). A higher value of k∗ was found for the floating media (55) compared with the value found for the sunken media (33). This indicated the greater efficiency of sCOD removal in the floating media. The values of the media constants were similar, showing the similarity in the media shape and size.

A rapid physical-chemical method for the determination of readily biodegradable soluble COD in municipal wastewater

A rapid physical-chemical method has been developed for the determination of the readily biodegradable portion of influent soluble COD. The method involves removal by flocculation and precipitation of colloidal matter that normally passes through 0.45 μm membrane filters. Results from four domestic wastewaters demonstrated that the physical-chemical method and the biological method (Ekama et al., 1984) gave virtually identical results. The physical-chemical method was used successfully to measure the quantity of truly soluble organic matter removed in the anaerobic zone of bench-scale enhanced biological phosphorus removal activated sludge systems.