The filtration characteristics of two different module configurations with coarse pore filter (non-woven fabric) were investigated for sludge floc separation in an activated sludge reactor for domestic wastewater reclamation. A polypropylene non-woven fabric filter (35 g/m2) was used for the two different module configurations, one flat and one tubular type, each with a filtration area of 0.052 m2. The different module types, submerged in the oxic compartment of A/O (anaerobic/oxic) type reactors, were operated simultaneously. The filtration fluxes were gradually increased from 0.5 to 1.2 and 1.73 m/d. The filtration pressures were more stably maintained for the tubular type module than the plate type. The tubular type module installed horizontally with two-side suction showed less filtration pressures than the tubular type module installed vertically with one-side suction. The solid separation was significantly high showing less than 5 mg/L effluent solids. The organic and T-N removal efficiencies were around 95 and 50%, respectively. The 85% removal of T-P was achieved with 20 mg/L injection of PAC (poly-aluminum chloride).
The performance of a treatment plant in reducing chlorine consuming substances as well as total trihalomethane formation (TTHM) could be evaluated rapidly using an accurate chlorine decay model as used in this study. The model could estimate the concentrations of fast and slow reacting agents (FRA and SRA–including organic and inorganic substances) and fast and slow reacting nitrogenous compounds (FRN and SRN) that are present in test waters. By estimating those concentrations in source and treated waters one could evaluate the performance of the treatment plant as well as provide options such as better catchment management for source water protection or treatment upgrades (e.g. enhanced coagulation) to remove chlorine consuming compounds which also have the potential to form THMs.
A rapid method using the pilot in-line filter to detect any change in coagulation performance was a proposed in this study. This method attempted to detect a change in coagulant dosage and mixing intensity by evaluating the filtrate quality of the in-line filter, which took the rapidly mixed water. Since the response time of this method was less than 10 min, it could be valuable to monitor the coagulation performance. The in-line filter was found more useful without underdrain. The in-line filter was more sensitive to a change in filtrate quality without underdrain than with underdrain. A new method, which combines a jar test with the in-line filter, was proposed to determine the coagulant dosage. This method reflected the actual plant situation more accurately than a jar test.
This study was undertaken to evaluate the suitability of microfiltration (MF) as pre-treatment for reverse osmosis (RO) seawater desalination to treat the seawater suffering from red-tide contamination using long-term operation of pilot plant. The one and a half year pilot MF operation had two objectives: stable production of the flow rate of 5 m3/h and acceptable water quality (SDI less than 3). The pilot plant operation revealed that the MF system successfully produced the target flow rate despite red-tide contamination of the seawater. The average flow rate of 5.2 m3/h was obtained at the average operating pressure of 0.53 bar. However, the MF system failed to achieve the target flow rate at red-tide bloom. When red-tide bloom occurred the chlorophyll-a concentration became 136 mg/m3, the flow rate decreased to half of the target, and energy consumption became extremely high. Subsequently, the operation was stopped. According to the relationship between the flow rate of the MF system and chlorophyll-a concentration developed in this study, it would be desirable to stop the MF operation at chlorophyll-a concentration of 57 mg/m3. The MF system produced acceptable quality water for RO feeding. The SDI of the MF treated was consistently less than 3. The MF system consumed 0.5 KWh of energy to produce 1 m3/h of MF treated, if the data during the red-tide bloom were excluded. Extra equipment (intake pump, control system, monitoring system, air conditioner) caused higher energy consumption than expected.
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