The characteristics of microbial ecosystem response with the changes of hydrolic retention time on an aerobic fixed-biofilm biological nutrient removal system

The influence of an aerobic fixed-biofilm activity, microbial ecosystem and mass transfer with respect to HRT variation in a BNR (biological nutrient removal) system has been investigated in this study. The process used in this study was an anoxic (1)/aerobic (1)/anoxic (2)/aerobic (2) system. The study was demonstrated by several kinds of techniques such as INT-dehydrogenase activity (DHA), INT (2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyl tetra-zolium chloride), DAPI (4’,6’-diamidino-2-phenylindole hydrochloride), and microelectrode. The study used by synthetic wastewater and HRT variation demonstrated that the DHA activity, density and heterotrophs/autotrophs ratio increased, as the HRT decreased from 8 hr to 4 hr. In comparing two aerobic reactors in fixed-biofilm process, the first aerobic reactor of the higher C/N ratio showed higher heterotrophs/autotrophs ratio and microbial activity than the second aerobic reactor. It was therefore concluded that the heterotrophs/autotrophs ratio and microbial activity were a greater influence on the first aerobic reactor, as organic loading rate was increased by HRT variation.     

Removal of nitrogen and phosphorus using a new biofilm process-INRS (Innovative Nutrient Removal System)

Adopting various process configurations may perform biological nutrient removal (BNR) from sewage. To get a compact BNR process, biofilm reactors were chosen for nitrification and denitrification. Enhanced biological nitrogen and phosphorus removal in a new fixed biofilm reactor was investigated in operation strategies with two reaction phases: anaerobic/anoxic/aerobic process with post-anoxic/aerobic biofilm process (Run 2A) and Run 2A with exogenous carbon sources for denitrifying and removing phosphorus (Run 2B). The influent used was “J” WWTP influent that consisted of wastewater from nearby a factory district area, leachate, and sewage. Therefore, the influent contained a great deal of refractory organic compound. The mean concentrations of COD, NH ₄ ⁺ -N and T-P in the influent were about 297.0 mg/L, 64.92 mg/L and 2.63 mg/L, respectively. The C: N: P ratio of influent was 113: 25: 1 and it was not suitable for growth of microorganism compared with 100: 5: 1 of proper growth C:N:P ratio. But, at a total HRT of the system of 16 hours in Run 2, the system worked successfully obtaining removal of COD, T-N and T-P of the case of Run 2A, 80.1 %, 74.9 %, and 50.8 %, respectively, and Run 2B(c) with exogenous carbon source (Na-acetate) obtained 86.2 % T-N removal efficiency. The results of this research showed that an innovative nutrient removal system (INRS) process packed with SAC media could be applicable for treatment of nutrients from municipal wastewater.     

Comparison of COD, nitrogen and phosphorus removal between anaerobic/anoxic/aerobic and anoxic/aerobic fixed biofilm reactor using SAC (Synthetic Activated Ceramic) media

In order to remove nitrogen and phosphorus simultaneously and to develop a compact process for retrofitting a conventional activated sludge system, a new fixed-biofilm reactor was designed and tested employing an operation strategy with three and two reaction phases : anaerobic/anoxic/aerobic (Run-1) and anoxic/aerobic (Run-2). Four kinds of HRT (4, 6, 8 and 10 h) were varied to investigate the effect of nitrification and denitrification in each reactor. The results of the experiments are summarized as follows. All removal rates of COD, T-N and T-P in the water treated in Run-1 were higher than those of Run-2. The average values of COD, T-N and T-P in the treated water were reduced to 5.0 mg/L, 5.6 mg/L and 3.1 mg/L in case of Run-1. The COD and T-N removal efficiencies of Run-1 were higher than that of Run-2, but the difference between Run 1 and Run 2 was almost negligible. More than 60 % T-P removal efficiency could be achieved when the HRT was above 8 hour, but the efficiency was sharply decreased to 36% as the HRT was decreased to 4 hour in case of Run-1. Although the removal efficiency of T-P in Run-2 decreased by 56 % compared with that of Run-1, the fixed biofilm reactor using SAC media reduced the volume of reactor, and high-level COD and T-N removal from domestic wastewater was performed ; stable effluent quality was thereby achieved. The performance of Run 2 with no anaerobic reactor was mostly similar to that of Run 1 with an anaerobic reactor, except for T-P removal. Hence, according to these results, anoxic and aerobic processes using SAC media could be possible for removing organics and nutrients from municipal wastewater, in case phosphorus removal is not considered for municipal wastewater with low concentration of phosphorus.     

Fenton oxidation process control using oxidation-reduction potential measurement for pigment wastewater treatment

The Fenton oxidation process was applied as a pretreatment process to degrade non-biodegradable organic matters in pigment wastewater. It was necessary to continuously measure the fluctuating concentration of organics in the pigment wastewater and to determine the amount of Fenton’s reagent required to oxidize the organics. Batch and continuous flow tests were used to evaluate the relationship between the concentration of organics (COD_Cr) and the amount of Fenton’s reagent required to achieve a sufficient oxidation of the organics. On-line measurements of the oxidation-reduction potential (ORP) value in the batch and continuous flow tests showed that the maximum ORP values were highly related to the organic concentrations (expressed as COD_Cr) and the Fenton’s reagent dosage (expressed as H₂O₂ concentration). The empirical equation was [COD_Cr]=8808+0.494[H₂O₂]-14.6ORP. A control program of Fenton’s reagent dosage based on the empirical equation was applied to control of a pilot scale Fenton oxidation process using ORP measurement. The concentration of organics predicted with the control program well agreed with the observed concentration of organics in the pigment wastewater. The variation of the effluent organics concentration of the controlled Fenton oxidation process was significantly reduced compared to that of a process without the control system. These results suggested that the control system of Fenton’s reagent dosage using ORP measurement would be applicable to the Fenton oxidation process for efficient pretreatment of pigment wastewater.