Effluent Chemical Oxygen Demand Concentration Research Articles

Methanotrophic bacteria for nutrient removal from wastewater: attached film system

ABSTRACT: It was hypothesized that nutrient removal from wastewater could be achieved by using methane oxidizing bacteria (methanotrophs). Because methane is inexpensive, it can be used as an energy source to encourage bacterial growth to assimilate nitrogen and phosphorus and other trace elements. This initial feasibility study used synthetic nutrient mixtures and secondary sewage effluent as feed to a laboratory‐scale methanotrophic attached‐film expanded bed (MAFEB) reactor operated at 35°C and 20°C. The MAFEB system operated successfully at low nutrient concentrations under a variety of nutrientlimited conditions. Using a synthetic nutrient mixture with a nitrogemphosphorus feed ratio(w/w) of 9:1, phosphate concentrations were reduced from 1.3 mg P/L to below 0.1 mg P/L, and ammonia was reduced from 12 mg N/L to approximately 1 mg N/L on a continuous flow basis, with a bed hydraulic retention time of 4.8 hours. The average nutrient uptake rates from synthetic nutrient mixtures were 100 mg nitrogen and 10 mg phosphorus/L of expanded bed/d. Nutrient assimilation rates increased with increasing growth rate and with increasing temperature. Nitrogen/ phosphorus uptake ratios varied from 8 to 13, and the observed yield varied from 0.11 to 0.16 g volatile solids (VS)/ g chemical oxygen demand (COD). Nutrient removal from secondary sewage effluent was successfully demonstrated using sewage effluent from two local treatment plants. Nutrient concentrations of 10‐15 mg N/L and 1.0‐1.8 mg P/L were reduced consistently below 1 mg N/L and 0.1 mg P/L. No supplemental nutrients were added to the sewage to attain these removal efficiencies since the nutrient mass ratios were similar to that required by the methanotrophs. Removal rates were lower at 20°C than at 35°C, but high removal efficiencies were maintained at both temperatures. Effluent suspended solids concentrations ranged from 8 to 30 mg volatile suspended solids (VSS)/L, and the effluent soluble COD concentration averaged 30 mg/L.

Treatment of a high‐strength, mixed phenolic waste in an SBR

ABSTRACT: Biological degradation of a synthetic mixture of several phenolic compounds typically found in coal conversion wastes was investigated in the sequencing batch reactor (SBR). The mixture contained phenol; o‐, m‐, and p‐cresols; and 2,3and 3,4‐dimethylphenols and had a total chemical oxygen demand (COD) concentration of 7750 mg/L. A variety of aerobic and anoxic control strategies were tested. A strategy that included an extended anoxic period resulted in the accumulation of byproducts that adversely affected removal efficiency and overall performance. In general, however, COD removal efficiencies were greater than 99%, with effluent COD concentrations averaging between 30 and 52 mg/L. Overdesign of the SBR (that is, hydraulic retention times in excess of that required for COD removal) resulted in the development of filamentous bacteria and poor settling characteristics in the reactor. This problem was eliminated or controlled either by introducing a short anoxic fill period or increasing the organic load. Removal patterns indicative of diauxic growth were observed. Conventional design approaches based on overall COD removal patterns and organic load must be applied cautiously and in conjunction with the removal patterns for individual components when used to design facilities that treat multicomponent toxic wastes.

Feasibility of activated sludge treatment of potato processing wastewaters

Laboratory studies were undertaken to determine the feasibility of using the activated sludge process in treating liquid effluents generated from a potato processing plant in the Red River Valley in North Dakota, USA. The wastewaters contained average COD (Chemical Oxygen Demand) and alkalinity concentrations of 1870 and 390 mg litre −1. Factors affecting the activated sludge treatment unit performance were evaluated in this study. These included the hydraulic detention time in the aeration tank, the sludge age, and the dosage of powdered activated carbon added to the aeration tank. The hydraulic detection time was varied from 0·35 to 1·42 days, and the sludge age ranged from 1·96 to 4·86 days. Activated carbon dosages of 4000 mg litre −1 were maintained in three reactors, while three other reactors were without carbon addition. Nutrient additions of nitrogen and phosphate were employed to achieve effective biological waste treatment. Biological treatment removed from 87 to 98% of ammonia-nitrogen to give final effluent concentrations between 1·1 and 5·6 mg litre −1. Reactors without carbon addition removed 92 to 94% of COD with an effluent COD of 114 to 147 mg litre −1. With the addition of carbon the COD removal efficiencies increased to 94 to 96% with an effluent COD concentration of 67 to 108 mg litre −1. Based on this study, the activated sludge process can be used effectively in treating potato processing wastewaters to achieve an effluent COD of less than 100 mg litre −1. The design parameters include a hydraulic detention time of 1·43 days, a sludge age of 5 days, and a powdered activated carbon dosage of 4000 mg litre −1.