Prayoon Fongsatitkul

Effects of dissolved oxygen on biological nitrogen removal in integrated fixed film activated sludge (IFAS) wastewater treatment process

The objective of this research was to determine the effects of dissolved oxygen on the biological nitrogen removal in the Integrated Fixed Film Activated Sludge (IFAS) and Modified Ludzack-Ettinger (MLE) systems. The carbonaceous and nitrogen removals were investigated at the COD/Nitrogen (C/N) ratios of 4, 6, and 10, and the dissolved oxygen (DO) concentrations of 2, 4, and 6 mg/L. The experimental results indicate that the C/N ratios of 4, 6, and 10 and the DO concentrations of 2, 4, and 6 affected insignificantly on the chemical oxygen demand (COD) removal, but significantly on the nitrogen removal as the consequences of different nitrification and denitrifcation rates in both systems. The COD removal was nearly completed throughout this study because glucose was used as a primary carbon source in the wastewater and both systems were operated at high SRT relative to the minimum SRT requirement for COD removal. The experimental conditions used in this study apparently led to nitrite accumulation in both IFAS and MLE systems. It is suggested that there is no benefit of installing media in the IFAS system at the C/N ratio of 10 because the system was underloaded with the nitrogen. The lower DO concentration, the greater denitrification in the anoxic zone was achieved because nitrite nitrogen was used as an electron acceptor. At the C/N ratios of 4 and 6, the IFAS system was higher in capacity for nitrification as a result of attached biomass on the support media in the aerobic zone. The DO concentration of 6 mg/L is required to maximize the nitrification rates in the systems under these experimental conditions resulting in greater oxidized nitrogen for denitrification in the anoxic zones. The denitrification in the aerobic zone of the IFAS system is not evaluated due to unavailability of nitrite information. The optimal DO concentrations for biological nitrogen removal in the IFAS system at the C/N ratios of 4, 6, and 10 in this study were 6, 6, and 2 mg/L, respectively.

Stability and capacity enhancements of activated sludge process by IFAS technology

This research was conducted to evaluate the capacity and stability of the Activated Sludge (AS) process retrofitted to the Integrated Fixed Film Activated Sludge (IFAS) process. Hydraulic retention time (HRT) and solids retention time (SRT) were used as independent variables in this investigation. The IFAS and AS processes were operated in parallel for carbon removal and nitrification at 6, 8, and 10 hours HRTs at which 4, 6, and 8 days SRTs were maintained. The AS system failed to attain steady state conditions at 10 hours HRT with 4 days SRT, 8 hours HRT with 4 and 6 days SRTs, and 6 hours HRT with 4, 6, and 8 days SRTs, whereas the IFAS system was stabilized until the SRT and HRT were at 4 days and 6 hours, respectively. Excessive filamentous microorganisms were observed in the IFAS and AS systems as the results of completely-mixed condition and high readily biodegradable organic content in the wastewater. The filamentous bulking was apparently the cause of system failure and the reduction of nitrification in the AS system. As the HRTs and SRTs were decreased or the system loadings increased, it was clearly demonstrated that the IFAS system was higher in capacity and stability than the AS system. The attached biomass in the IFAS system suppressed the growth of filamentous microorganisms by reducing the amount of substrates in contact with the filamentous microorganisms providing the system stability. Nitrification was completed in the IFAS system and could be independent of the suspended SRT. Both AS and IFAS systems could provide the same performance for COD removal at the experimental conditions.

Effect of mixture ratio, solids concentration and hydraulic retention time on the anaerobic digestion of the organic fraction of municipal solid waste.

This paper describes how the degradation of the organic fraction of municipal solid waste (OFMSW) is affected through codigestion with varying amounts of return activated sludge (RAS). Solid waste that had its inorganic fraction selectively removed was mixed with RAS in ratios of 100% OFMSW, 50% OFMSW/50% RAS, and 25% OFMSW/75% RAS. The total solids (TS) concentration was held at 8% and three anaerobic digester systems treating the mixtures were held (for the first run) at a total hydraulic retention time (HRT) of 28 days. Increasing amounts of RAS did not however improve the mixture’s digestability, as indicated by little change and/or a drop in the main performance indices [including percentage volatile solids (VS) removal and specific gas production]. The optimum ratio in this research therefore appeared to be 100% OFMSW with an associated 85.1 ± 0.6% VS removal and 0.72 ± 0.01 L total gas g- 1 VS. In the second run, the effect of increasing percentage of TS (8, 12% and 15%) at a system HRT of 28 days was observed to yield no improvement in the main performance indices (i.e. percentage VS removal and specific gas production). Finally, during the third run, variations in the total system HRT were investigated at an 8% TS, again using 100% OFMSW. Of the HRTs explored (23, 28 and 33 days), the longest HRT yielded the best performance overall, particularly in terms of specific gas production (0.77 ± 0.01 L total gas g-1 VS).

Two-phase anaerobic digestion of the organic fraction of municipal solid waste: estimation of methane production

Energy generation from methane (CH4) is one of the primary targets of the anaerobic digestion process. Consequently, the focus of this study was to investigate the effect on CH4 production of total solids (TS) loading (measured as % TS) and hydraulic residence time (HRT) during the treatment of the organic fraction of municipal solid waste (OFMSW). Laboratory-scale, two-phase anaerobic digestion systems were employed with each system consisting of an acidogenic reactor and a methanogenic reactor linked in series. The group A runs in the experiment explored the effect on digester performance of four variations in methanogenic HRT (15, 20, 25 and 30 days) at three different feed TS concentrations (8, 12 and 15%). The group B runs compared the actual methane yield (0.14 to 0.45 L g VS feed − 1 ) to that predicted by the Chen–Hashimoto model. Results from the group A runs indicated that acidogenesis improved with an increase in % TS and a decrease in HRT; while, methanogenesis behaved inversely, achieving higher yields at the lower % TS and longer HRT values. In comparison with the group B runs, the Chen–Hashimoto model under-predicted (by an average of 16.5 ± 6.6%) the CH4 yield obtained from the digestion of OFMSW.

TREATMENT OF FOUR INDUSTRIAL WASTEWATERS BY SEQUENCING BATCH REACTORS : EVALUATION OF COD, TKN AND TP REMOVAL

Abstract This study investigated the ability of a sequencing batch reactor (SBR) system to treat four industrial wastewaters, namely, textile, landfill leachate, seafood and slaughterhouse effluents. The system employed three identical SBRs (10 l volume each) operating in parallel and each waste was treated one at a time. The operational variables examined included the length of the non‐aerated period and the solids retention time (SRT). All four wastewaters experienced chemical oxyfen demand (COD) and total kjeldhal nitrogen (TKN) removals greater than 81%, while the TP removals were lower, ranging from 57 to 94%. The length of the non‐aerated period appeared to have minimal effect on the SBR performance; however, increases in SRT reduced the percent TP removal for the textile and leachate wastes only. In addition, to investigate organic loading limits to the seafood SBR system, the COD was increased by three increments of 250 mg l−1 starting from a baseline concentration of 1100 mg l−1. This resulted in a reduction in both the TKN and TP removal at the higher concentrations. Finally, for the slaughterhouse wastewater, the COD:TKN ratio was tested at levels of 6:1, 8:1 and 9:1 with the result that only the TP removal was affected at the lowest ratio.

Treatment of a slaughterhouse wastewater: effect of internal recycle rate on chemical oxygen demand, total Kjeldahl nitrogen and total phosphorus removal

This study investigated the ability of an anaerobic/anoxic/oxic (A2/O) system to treat a slaughterhouse wastewater. The system employed two identical continuous-flow reactors (10 l total liquid volume each) running in parallel with the main operational variable, being the internal recycle (IR) rate. The chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN) and total phosphorus (TP) performance was evaluated as the IR flowrate was increased from a Q of 15 l d−1 to 4Q at a system hydraulic retention time of 16 h and a solids retention time of 10 d. The COD:TKN and COD:TP ratios were 8.2:1 and 54:1, which supported both nitrogen and phosphorus removal. For all IR multiples of Q, the COD removal was in excess of 90%. The TKN removal showed a modest improvement (a 4–5% increase, depending on the dissolved oxygen (DO)) as the IR doubled from Q to 2Q, but no further increase was observed at the 4Q IR rate. The TP removal reached its optimum (around 85%–89% (again depending on the DO)) at the 2Q rate.

The influence of organic loading and anoxic/oxic times on the removal of carbon, nitrogen and phosphorus from a wastewater treated in a sequencing batch reactor

In this study, 10 L sequencing batch reactors (SBRs) were operated at a 12-h cycle length (four alternating anoxic/oxic conditions) to assess the biological nutrient removal potential of a domestic wastewater treated at the Huay Kwang plant, Bangkok, Thailand. The wastewater was found to be carbon-limited (chemical oxygen demand (COD) to total Kjeldahl nitrogen (TKN) (i.e., COD:TKN) ratio of 6.4:1). This ratio was insufficient to support good phosphorus removal. Glucose was therefore added to increase the COD:TKN ratio ultimately to 10:1 and the COD, TKN and total phosphorus (TP) removals at this ratio were all in excess of 95%. An alternative carbon source from a local fruit canning industry was then added at the same COD:TKN ratio; and, in order to increase the throughput of the waste treated, the cycle length was simultaneously shortened to 8 h keeping approximately the same anoxic/oxic fractions. The COD removal remained high (> 95%), however the TKN and TP removals were substantially reduced (79% and 66%, respectively), indicating that the shortened cycle length was sub-optimum. The last phase of the research involved changing the anoxic/oxic fractions of the cycle time to maximize performance. It was found that for the conditions studied in this research, the performance improved in proportion to the increase in the first anoxic fraction, being most stable at the highest anoxic fraction of the cycle length (0.33).

Treatment of a Textile Dye Wastewater by an Electrochemical Process

This study explored the effectiveness of an electrochemical process to treat a sulfur dye wastewater from a textile industry. The treatment system included a 4.0 L reactor equipped with five steel electrode plates, and a separate sedimentation tank of equal liquid volume. The experimental part involved two distinct, sequential stages. In the first stage, the effect of initial pH and electrical charge (i.e., current times reaction time) on the treatment process was explored. Experiments were conducted in a factorial mode, involving three initial pH values (3, 4 and 5), and six electrical charges (ranging from 150 to 1,350 coulomb), respectively. Results indicated that chemical oxygen demand (COD), total suspended solids (TSS), and color removal efficiency improved with a decrease in initial pH and an increase in electrical charge. Overall, high percent removal values were observed ranging from 63% to 80% for COD, 81% to 96% for TSS, and 93% to 99% for color. During the second stage, the electrode corrosion pattern was investigated for a period of 45 days. Under stable operating conditions, electrode consumption was found to conform to Faradays law. Moreover, process performance regarding COD, TSS, and color reduction was comparable to that obtained in the first stage of the study.

Development of statistical models for trihalomethane (THM) occurrence in a water distribution network in Central Thailand

This study initially investigated the occurrence of trihalomethanes (THMs) in the water supply system of Metropolitan Bangkok, Thailand, evaluating 624 samples collected between 2007 and 2009. It was found that the mean total THM concentration was 66 μg/L, with CHCl3 accounting for 85% of the total. The main focus, however, was the development of models using linear and non-linear regression analyses to determine the effect of key disinfection parameters on THM formation. Regression techniques revealed that the total and residual Cl2 concentrations, and contact time (expressed as the equivalent pipe distance) played the most critical role in THM formation, regardless of the season investigated. A moderate correlation was generally observed, however, the correlation was considerably stronger in the dry seasons (i.e. winter and summer) compared to the rainy season. Furthermore, the similarity in statistical parameters regarding the actual and predicted THM concentrations suggests that the models developed are reliable.

Co-treatment of domestic and dairy wastewater in an activated sludge system.

This research assesses the potential for co-treatment of a dairy wastewater with a domestic wastewater in a lab-scale, continuous-flow, activated sludge system. To evaluate the influence of the dairy waste contribution, seven runs were conducted with each run being a mixture of dairy wastewater (either cheese or milk) in different ratios ranging from 1:0.01 to 1:0.30 by volume. More than 87% of the carbon was removed for both waste additions; however, while 95% ammonia-nitrogen removal was recorded for the cheese waste, only 75% removal was obtained for the milk. Kinetic studies for carbon consumption revealed a first-order model with lower kinetic constants as the cheese waste proportion increased. Specific carbon consumption rates indicated that the biomass had not reached its maximum potential to degrade carbon. The ability of the biomass to settle was hindered when the Gram negative to Gram positive filamentous bacteria ratio increased to approximately 1.5.