Adjusting Chlorine Dosage and to Prevent Bio‐Growth and Minimize Trihalomethanes in Reverse Osmosis Filtrate in a Wastewater Reclamation Process

Abstract

Feasibility of effluent reclamation for the Futian municipal WWTP in Taichung Taiwan was evaluated using an “SF‐UF‐RO” pilot plant. The optimal parameters of each unit were obtained during the pilot plant test. The pilot plant started the operation in late October 2008 and operated until January 2011. The reverse osmosis (RO) system produces 75 m3 water daily, and the produced water quality was comparable to the city water in Taichung. Chlorine dosed in the sand filtration (SF) inlet and ultrafiltration (UF) backwash had the most significant effect on the stability of system performance. When the chlorine was underdosed, biofilm clogged the bag filter (prefilter of UF) and led to the flow rate decay of the UF. The prefilter needed replacement every 1 or 2 weeks resulting in increased process cost. On the other hand, when the chlorine dosage was increased to mitigate the biofilm growth, the residual chlorine not only reacted with TOC and derived trihalomethanes (THMs) in the RO product water (more than 20 µg/L), but it also damaged the RO membrane. After trial and error, the chlorine concentration was optimized as 0.7 mg/L in SF inlet to prevent growth of biofilm as well as to control the residual chlorine in the RO inlet and THMs in the RO product water. It is suggested that cautiously adjusting chlorine dosage is essential for stably operating such a hybrid membrane system to reclaim the municipal wastewater.

Assessment of Municipal Effluent Reclamation Process Based on the Information of Cost Analysis and Environmental Impacts

“…The pilot testing provides the results including permeate flux of individual units, requirement of chemicals and consumables, and electricity consumption. More information was given in the studies of Hsu et al [16,17]. By referring to the inquiry from the membrane module manufacturers, cost analysis was conducted to estimate the capital requirement of building large-scale plant for reclaiming the effluent.…”

The Effect of Membrane Treatment on Chlorine Decay and Trihalomethanes Formation in Water Distribution Systems

“…Chlorine, because of its superiority of low cost, stability, and effectiveness, has been widely used for disinfection. However, amounts of natural organic matter (NOM) can react with chlorine to form disinfection byproducts (DBPs), such as trihalomethanes (THMs) and haloacetic acids (HAA), which have been proved to deteriorate the water quality [2]. Because of its decay, chlorine concentration decreases with time and the by-product concentrations also vary within the water distribution systems.…”