Shun-Hsing Chuang

Modeling biogas production from organic fraction of MSW co-digested with MSWI ashes in anaerobic bioreactors

This study aims at investigating the effects of MSW incinerator fly ash (FA) and bottom ash (BA) on the anaerobic co-digestion of OFMSW with FA or BA. It also simulates the biogas production from various dosed and control bioreactors. Results showed that suitable ashes addition (FA/MSW 10 and 20 g L(-1) and BA/MSW 100 g L(-1)) could improve the MSW anaerobic digestion and enhance the biogas production rates. FA/MSW 20 g L(-1) bioreactor had the higher biogas production and rate implying the potential option for MSW anaerobic co-digestion. Modeling studies showed that exponential plot simulated better for FA/MSW 10 g L(-1) and control bioreactors while Gaussian plot was applicable for FA/MSW 20 g L(-1) one. Linear and exponential plot of descending limb both simulated better for BA/MSW 100 g L(-1) bioreactor. Modified Gompertz plot showed higher correlation of biogas accumulation than exponential rise to maximum plot for all bioreactors.

The effects of soluble organic matters on membrane fouling index

This study investigated the effects of soluble organic matters on membrane fouling characteristics, using silt density index (SDI) and modified fouling index (MFI) to evaluate the fouling potential. Experimental results demonstrated that humic acid had significant effects on membrane fouling indexes. When its concentration was in the range of 0.01-0.05 mg/L, the SDI(15) and MFI were 2.9-3.9 and 5.4-13.8s/L(2), respectively. According to the linear equations of MFI measurements, the fouling potential was in the order of humic acid>nucleic acid protein>glucose. Moreover, the molecular weight of dextran played an important role in membrane fouling indexes. Furthermore, a mathematical analysis of filtration experiments based on saturation curve was developed in this study. The maximum accumulated filtrate (V(max)) and the constant of filtration (k(f)) could be obtained to improve the precision of membrane fouling prediction.

Effects of different carbon supplements on phosphorus removal in low C/P ratio industrial wastewater.

This study focuses on the effects of different carbon supplements on biological phosphorus removal in the optonics and semiconductor industrial wastewater treatment. Experimental results demonstrate that the addition of a carbon source (glucose, acetate, and digester supernatant) improved phosphorus removal effectively. When the COD/P ratios were controlled in the range of 18-20 (using glucose and supernatant as supplement), the acclimated sludge showed more than 98% removal of phosphorus. In addition, different organic carbons induce dissimilar behavior in anaerobic release and aerobic uptake of phosphorus. The glucose supplement induces significant phosphorus release in anaerobic phase and then an increased phosphorus uptake in aerobic phase. The released phosphorus descended in anaerobic phase when acetate and supernatant were added. There was a good linear relationship of first order reaction between initial COD concentration and specific substrate utilization rate in anaerobic phase.

Dynamic fouling behaviors of submerged nonwoven bioreactor for filtration of activated sludge with different SRT

The flux variations and resistances accumulated during filtration of activated sludge with sludge retention time (SRT) of 15, 30, and 60 days were analyzed to investigate the dynamic fouling behavior in a submerged nonwoven bioreactor. Different SRT values varied sludge condition and particle size distribution in the supernatants, which caused dissimilar fouling characteristics. Short-term fouling of the nonwoven bioreactor during filtration of activated sludge with SRT of 15 days was fully reversible, and the resistance percentages of solutes, colloids, and suspended solids were 6%, 27%, and 67%, respectively. On the other hand, significant increases of colloid resistance, such as with the filtration of activated sludge with SRT of 30 and 60 days, were related to the occurrence of irreversible fouling. The phenomenon of pore blocking by particles or colloids with size analogous to the pore of nonwoven fabric was a decisive factor leading to irreversible fouling in the large-pore materials.

Biotreatment of sulfate-rich wastewater in an anaerobic/micro-aerobic bioreactor system

The focus of this study was on sulfate-rich wastewater treatment in a novel anaerobic / micro-aerobic bioreactor system. The system was composed of an upward-flow anaerobic sludge blanket (UASB) reactor and a floated bed micro-aerobic reactor, which was packed with elastic porous carriers and was controlled in a situation of dissolved oxygen below 0.5 mg l−1. The floated bed micro-aerobic reactor was developed for accumulating a higher amount of biomass in carriers with a short hydraulic retention time (HRT) for biological oxidation of hydrogen sulfide to elemental sulfur. During long-term steady state operation, experimental results showed that an average of 70±6% of sulfate was transformed to hydrogen sulfide in UASB reactor. Moreover, the overwhelming majority of sulfide was oxidized to elemental sulfur and sulfate in micro-aerobic reactor; and the recirculation of effluent to UASB reactor reduced effectively the degree of inhibition caused by sulfate-rich wastewater. In UASB reactor, chemical oxygen demand (COD) removal efficiency increased with COD loading, in contrast, the performance of sulfate removal decreased with the increase in sulfate loading in a range of 1.0-1.75 kg SO4 2− m−3 d−1. In micro-aerobic reactor, sulfide was removed almost completely under the operation of HRT 2.8 h. Furthermore, experimental results of continuous operations revealed that oxidation-reduction potential (ORP) was an adequate parameter for controlling biological oxidation of sulfide. When ORP was regulated in a lower range of −250 to −300 mV, the amount of regenerated sulfate was reduced significantly in micro-aerobic reactor.

Improving the removal of anions by coagulation and dissolved air flotation in wastewater reclamation

This study investigated the feasibility of improving the removal of anions from a secondary effluent by coagulation/flocculation (Coag/Floc) and dissolved air flotation (DAF) using a pilot-scale wastewater reclamation plant in a high-tech industrial park. The pilot plant was equipped with units of Coag/Floc, DAF, activated carbon beds (AC), micro-filtration modules (MF) and a reverse-osmosis membrane (RO). It was operated in-situ continuously for around one year to evaluate the performance of anion removal in two processes - the AC-RO process and the DAF-AC-RO process. Long-term experimental results indicated that combining Coag/Floc, DAF and AC units increased the potential of pretreatment to remove anions. The removal efficiencies in Coag/Floc-DAF units were in the order phosphate > fluoride > chloride > sulfate > silicate. The charged complex of PACl flocs revealed a higher affinity for adsorption onto phosphate and fluoride than on chloride, sulfate and silicate. Comparison of the performance of Coag/Floc-DAF-AC units in the DAF-AC-RO process with that of a single AC unit in the AC-RO process demonstrated that adding Coag/Floc-DAF units increased the removal efficiencies of phosphate, fluoride and silicate by approximately 70.0 %, 42.7 % and 70.1 %, respectively. Most of the phosphate and fluoride were removed in Coag/Floc-DAF units, while most of the silicate escaped from the Coag/Floc-DAF units, and was adsorbed and/or trapped in the AC unit. The quality of reclaimed water in the DAF-AC-RO process complied with the requirements of high-tech industries in cleaning processes. Combined units of Coag/Floc-DAF-AC were therefore recommended for use in pretreatment in wastewater reclamation in high-tech industrial parks.

Comparison of polyhydroxyalkanoates production by activated sludges from anaerobic and oxic zones of an enhanced biological phosphorus removal system: effect of sludge retention time

This study compared the PHAs production behavior of sludges from the anaerobic and oxic phases of an enhanced biological phosphorus removal (EBPR) system. This was accomplished by using the kinetics and stoichiometric coefficients obtained from aerobic batch tests to evaluate the performance of these two sludges. Experimental results indicated that the metabolic behavior of the sludges for PHAs production depend significantly on the operating sludge retention time (SRT) of the EBPR system. The oxic sludge with 5 days of SRT exhibited better PHAs production performance than anaerobic sludge. Conversely, the anaerobic sludge with 15 days of SRT had superior PHAs production capability compared to oxic sludge. These comparisons suggest that whether anaerobic or oxic sludge should be employed for PHAs production depends mainly on the operating SRT of the EBPR system.

Phosphorus Removal Characteristics of a Combined As-Biofilm Process Cultured by Different COD/TP Ratios

The COD/TP ratio of influent is an important parameter for the phosphorus removal in a biological nutrient removal (BNR) process. In this study, we investigated the phosphorus removal and denitrification characteristics of a combined activated sludge-biofilm process, as cultured by different influent COD/TP ratios ranged from 12 to 120. Experimental results indicated that, when COD/TP ratios exceeded 30, the removal efficiencies of COD, TN and TP were 98%, 76% and 100%, respectively. However, when the COD/TP ratios were less than 30, the COD removal efficiency still surpassed 98%, but the TP removal efficiency decreased to 41% and 31.8% when COD/TP ratios were 20 and 12. Moreover, the weight percentage of phosphorus in the sludge attained a stable value when the COD/TP ratios were below 30. The maximum weight percentage of phosphorus in the sludge was found to be about 6% and, under this condition, the critical COD/TP ratio of influent was 30 of the process under a sludge retention time of 12 days. Although the amount of accumulated PHAs per mg phosphate released (γPHA/PO4) remained stable between a COD/TP ratio of 30 to 120, it increased with a decreased of the COD/TP ratio when the COD/TP ratio was less than 30.