Kang-Woo Cho

Monitoring the microbial community shift throughout the shock changes of hydraulic retention time in an anaerobic moving bed membrane bioreactor

An anaerobic moving bed membrane bioreactor (AnMBMBR) fed with synthetic domestic wastewater was investigated under hydraulic retention time (HRT) shocks to assess the effects on the microbial (bacteria and archaea) community and reactor performance. 16S rDNA targeted polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) approach was optimized to relate the metabolic and community composition with biogas generation, methane content and COD removal efficiency. From the drastic decrease of HRT (from 8 h to 4 h), the methane production was significantly reduced due to the HRT shock, while the COD removal efficiency was not affected. The enhanced growth of homoacetogenic bacteria, Thermoanaerobacteraceae competes with methanogens under shock period. When the HRT was recovered to 8 h, the methane generation rate was higher than the initial operation before the shock HRT changes, which would be ascribed to the activity of new emerging hydrogenotrophic archaea, Methanocella sp. and Methanofollis sp.

Enhanced biological nitrogen removal in MLE combined with post-denitrification process and EF clarifier

A modified ludzack ettinger reactor (MLE) combined with a post-denitrification reactor (PDMLE) using electroflotation (EF) as a secondary clarifier was investigated on its feasibility and process performance. Results indicated that higher mixed liquor suspended solids (MLSS) concentrations in bioreactor (5,350xa0±xa0352xa0mg L−1) were maintained via the highly concentrated return sludge (16,771xa0±xa0991xa0mg L−1) from the EF clarifier and the effluent suspended solids (SS) concentrations continued relatively low, representing effluent SS concentration of 1.71xa0±xa01.16xa0mg L−1, compared with GS-A2O process during the operation of four months. The denitrification was improved by combining MLE process with post-denitrification based on endogenous decay (i.e. no additional carbon source was added), resulting in the removal efficiencies of TN were about 91 and 59% for the influent C/N ratio of 10 and 5, respectively, revealing relatively high nitrogen removal as compared with EF-A2O and gravity settling (GS)-A2O processes as a control. The nitrogen balance analysis indicates that pre-denitrification and post-denitrification contributed to 78 and 22% of TN removed, respectively.

Feasibility of electroflotation to separate solids and liquid in an activated sludge process

In this study, electroflotation (EF) has been applied as a secondary clarification in the activated sludge process to improve the efficiency of the solids–liquid separation, which is essential in maintaining effluent quality. The effects of sludge settleability were examined through a series of batch and semi‐continuous experiments. The results of the batch experiments revealed that thickening efficiencies using EF were 2.6 to 9.2 times higher than those with gravity settling (GS). In addition, clarification efficiencies were not significantly influenced by sludge settling properties, as compared with GS as a control. In the semi‐continuous EF experiments, the concentrations of solids in the float layer were maintained above 10 g L−1 during flotation, regardless of variations in sludge settleability. Furthermore, the volumetric gas proportion in the float layer increased as the gas to solids (G/S) ratio rose. This allowed the float layer to be more stably suspended against gravity at the top of the reactor. Based on the results obtained from these batch and semi‐continuous experiments, an anoxic/oxic (AO) reactor combined with EF clarifier remained in successful continuous operation for four months. In comparison with conventional AO processes using a GS clarifier, enhanced clarification and thickening efficiencies were achieved through the EF–AO system. In addition, higher mixed liquor suspended solids concentrations (averaging 5300 mg L−1) in the bioreactor (EF–AO) were maintained via the return of highly concentrated sludge (averaging 16,400 mg L−1) from the EF clarifier. These findings suggest that EF could be a promising and effective alternative for the solids–liquid separation of poorly settling sludge.

The effects of antecedent dry days on the nitrogen removal in layered soil infiltration systems for storm run‐off control

The effects of antecedent dry days (ADD) on nitrogen removal efficiency were investigated in soil infiltration systems, with three distinguishable layers: mulch layer (ML), coarse soil layer (CSL) and fine soil layer (FSL). Two sets of lab‐scale columns with loamy CSL (C1) and sandy CSL (C2) were dosed with synthetic run‐off, carrying chemical oxygen demand of 100 mg L−1 and total nitrogen of 13 mg L−1. The intermittent dosing cycle was stepwise adjusted for 5, 10 and 20 days. The influent ammonium and organic nitrogen were adsorbed to the entire depth in C1, while dominantly to the FSL in C2. In both columns, the effluent ammonium concentration increased while the organic nitrogen concentration decreased, as ADD increased from 5 to 20 days. The effluent of C1 always showed nitrate concentration exceeding influent, caused by nitrification, by increasing amounts as ADD increased. However, the wash‐out of nitrate in C1 was not distinct in terms of mass since the effluent flow rate was only 25% of the influent. In contrast, efficient reduction (>95%) of nitrate loading was observed in C2 under ADD of 5 and 10 days, because of insignificant nitrification in the CSL and denitrification in the FSL. However, for the ADD of 20 days, a significant nitrate wash‐out appeared in C2 as well, possibly because of the re‐aeration by the decreasing water content in the FSL. Consequently, the total nitrogen load escaping with the effluent was always smaller in C2, supporting the effectiveness of sandy CSL over loamy FSL for nitrogen removal under various ADDs.

Electroflotation clarifier to enhance nitrogen removal in a two-stage alternating aeration bioreactor

Stringent water treatment criteria and rapidly growing pollutant loads provoke the demand for retrofitting wastewater treatment plants towards a higher capacity. In this study, we assess a two stage alternating aeration (AA) bioreactor equipped with electroflotation (EF) clarifier, for nitrogen removal within a short hydraulic reTENTion time (HRT). The EF under steady solids loading required a minimum unit height and gas:solids ratio of 0.006 for efficient clarification. The separated sludge blanket was further thickened with retaining stability when the cyclic solids loading was smaller than 1.0 kg m−2. In the continuous operation of the bioreactor, the returned activated sludge concentration increased to more than 18,000 mg L−1, while the effluent suspended solids concentration was lowered below 5 mg L−1. Under influent chemical oxygen demand (COD)/total inorganic nitrogen (TIN) concentration of 300/30 mg L−1, the TIN removal efficiency was near 70% with cycle time ratios of 0.17 and 0.27. Under higher influent COD concentration of 500 mg L−1, TIN removal efficiency was found to be 73.4% at a carbon:nitrogen (C:N) ratio of 10 and even higher (80.4%) at a C:N ratio of 16.6. The increased mixed liquor suspended solids concentrations (>6000 mg L−1) under the high COD loading were efficiently maintained by using the EF clarifier. The results of this study demonstrate that an EF clarifier with a HRT of less than 1 h can support reliable nitrogen removal in the AA process that has a HRT of 6 h, even under increasing influent loadings.

Development of a Self-Contained, PV-Powered Domestic Toilet and Electrochemical Wastewater Treatment System Suitable for the Developing World

We have developed a transportable prototype designed for the treatment of raw domestic wastewater, human urine, human feces, and synthetic human waste analogues. After several hours of PV-powered electrochemical treatment, the turbid, black-water influent can be clarified with the elimination of the suspended particles along with the reduction or total elimination of the chemical oxygen demand (COD), total enteric coliform disinfection via in situ reactive chlorine species generation, and the elimination of measurable protein after 3 to 4 hours of PV-powered treatment. Our advanced prototype incorporates additional features such as a residual sludge handling unit, a hydrogen purification and filter system, a closed water reuse We have packaged our second-generation prototypes into modified shipping containers are ready for field testing in remote locations that lack traditional urban infrastructure.