Nutrient removal in an A2O-MBR reactor with sludge reduction
ABSTRACT
In the prent study, an advanced wage treatment process has been developed by incorporating excess sludge reduction and phosphorous recovery in an A2O-MBR process. The A2O-MBR reactor was operated at a flux of 77 LMH over a period of 270 days. The designed flux was incread stepwi over a period of two weeks. The reactor was operated at two different MLSS range. Thermo chemical digestion of sludge was carried out at a fixed pH (11)and temperature (75℃) for 25% COD solubilisation. The relead pbospborous was recovered by precipitation process and the organics was nt back to anoxic tank. The sludge digestion did not have any impact on COD and TP removal efficiency of the reactor. During the 270 days of reactor operation, the MBR maintained relatively constant transmembrane pressure. The results bad on the study indicated that the propod process configuration has potential to reduce the excess sludge production as well as it didn't detonated the treated water quality.
Keywords: scotlandA2O reactor; MBR; Nutrient removal; TMP
1. Introduction
Excess sludge reduction and nutrients removal are the two important problems associated with wastewater treatment plant. MBR process has been known as a process with relatively high decay rate and less sludge production due to much longer sludge age in the reactor (Wen et al., 2004). Sludge production in MBR is reduced by 28-68%, depending on the sludge age ud (Xia et al.,
2008). However, minimizing the sludge production by increasing sludge age is limited due to the potential adver effect of high MLSS concentrations on membrane (Yoon et al., 2004). This problem can be solved by introducing sludge disintegration technique in MBR (Young et al., 2007). Sludge disintegration techniques have been reported to enhance the biodegradability of excess sludge (Vlyssides and Karlis, 2004). In overall, the basis for sludge reduction process is effective combination of the methods for sludge disintegration and biodegradation of treated sludge. Advances in sludge disintegration tec
hniques offer a few promising options including ultrasound (Guo et al., 2008), pul power (Choi et al.,2006), ozone (Weemaes et al., 2000), thermal (Kim et al., 2003),上海新东方 alkaline (Li et al., 2008) acid (Kim et al., 2003) and thermo chemical
(Vlyssides and Karlis, 2004). Among the various disintegration techniques, therm开工奠基仪式o chemical was reported to be simple and cost effective (Weemaes and Verstraete, 1998). In thermal-chemical hydrolysis, alkali sodium hydroxide was found to be the most effective agent in inducing cell lysis (Rocker et al., 1999).
Conventionally, the nutrient removal was carried out in an A2O process. It has advantage of achieving, nutrient removal along with organic compound oxidation in a single sludge configuration using linked reactors in ries (Tchobanoglous et al., 2003). The phosphoroes removal happens by subjecting phosphorous accumulating organisms (PAO) bacteria under aerobic and anaerobic conditions (Akin and Ugurlu, 2004). The operating procedures enhance predominance PAO, which are able to uptake phosphorous in excess. During the sludge pretreatment process the bound phosphoro
us was solubilid and it increas the phosphorous concentration in the effluent stream (Nishimura, 2001).So, it is necessary to remove the solubilid phosphorus before it enters into main stream. Besides, there is a growing demand for the sustainable phosphorous resources in the industrialized world. In many developed countries, rearches are currently underway to recover the phosphoroes bound in the sludge's of enhanced biological phosphorus removal system (EBPR). The relead phosphorous can be recovered in usable products using calcium salts precipitation method. Keeping this fact in mind, in the prent study, a new advanced wastewater treatment process is developed by integrating three process, which are: (a) thermo chemical pretreatment in MBR for excess sludge reduction (b) A2O process for biological nutrient removal (c) P recovery through calcium salt precipitation. The experimental data obtained were then ud to evaluate the performance of this integrated system.
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2. Methods
2.1. Wastewater
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The synthetic domestic wastewater was ud as the experimental influent. It was basically compod of a mixed carbon source, macro nutrients (N and P), an alkalinity control (NaHCO3) and a microelement solution. The composition contained (/iglL) 210 mg gluco, 200 mg NH4C1, 220 mg NaHCO3, 22一34 mg KH2POthe one you love4, microelement solution (0.19 mg MnCl2 4H20, 0.0018 mg ZnCl22H2O, 0.022 mg CuCl2 2H2O, 5.6 mg MgSO4 7H2O, 0.88 mg FeCl36H2O, 1.3 mg CaCl2 ·2H2O). The synthetic wastewater was prepared three times a week with concentrations of 210 ±1.5 mg/L chemical oxygen demand (COD), 40±1 mg/L total nitrogen (TN) and 5.5 mg/L total phosphorus (TP).
2.2. A2O-MBR
The working volume of the A2O银河护卫队2彩蛋-MBR was 83.4 L. A baffle was placed inside the reactor to divide it into anaerobic (8.4 L) anoxic世上没有免费的午餐 (25 L) and aerobic basin (50 L). The synthetic wastewater was feed into the reactor at a flow rate of 8.4 L/h (Q) using a feed pump. A liquid level nsor, planted in aerobic basin of A2O-MBR controlled the flow of influent. The HRT of anaerobic, anoxic and aerobic basins were 1, 3 and 6 h, respectively. In orde
r to facilitate nutrient removal, the reactor was provided with two internal recycle (1R). IRl (Q= 1)connects anoxic and anaerobic and IR 2 (Q=3) was between aerobic and anoxic. Anaerobic and anoxic basins were provided with low speed mixer to keep the mixed liquid suspended solids (MLSS) in suspension. In the aerobic zone, diffurs were ud to generate air bubbles for oxidation of organics and ammonia. Dissolved oxygen (DO) concentration in the aerobic basini sing was maintained at 3.5 mg/1 and was monitored continuously through online DO meter. The solid liquid paration happens in
