Treatment Of Wastewater From Swine Farms Using Submerged Membrane Bioreactor

China is a large pig production country, pig farms produce large amount of waste water with high contents of pollutants owing to the physiological characteristics of pigs and the current production systems. The environmental problems incurred by waste water severely restraint the sustainable development of pig industry. The croplands surrounding most pig farms are insufficient to receive waste water via land application, therefore, technologies of advanced wastewater treatment are in compelling needs In view of the lack of baseline data of wastewater characteristics and advanced treatment technologies, this study was conducted to: 1) measure the investigate the characteristics of wastewater from pig farms with different manure collection systems; 2) investigate the effects of membrane bioreactor(MBR) on the treatment of wastewater from pig farms with manual dry-collection system; 3) to design a pilot MBR system for the treatment of wastewater from swine farms. The results are as following:1. Selecting 3 typical swine farms with manual dry-collection system, deep-pit system and mechanical dry-collection system, respectively. Wastewater samples from all the farms were collected in 5 days continuously in each of the four seasons. The concentrations of COD, ammonia nitrogen(NH4+-N), total nitrogen(TN) and total phosphorate(TP) were measured during the experimental periods. The results showed that For the swine farms with manual dry-collection system, deep-pit system and mechanical dry-collection system, the annual mean concentrations of COD, of the wastewater were(3206±1020)mg/L,(16672±8212)mg/L and(18589±4871) mg/L, respectively; the annual means of TN were(328±119) mg/L,(2110±943) mg/L and(6249±2043) mg/L, respectively; the yearly averages were(185±64)mg/L,(1143±566) mg/L, and(2259±1240) mg/L, respectively; and the TP contents averaged(69±49)mg/L,(299±121)mg/L, and(104±75) mg/L, respectively. For the 3 manure collection systems, the COD, TN and NH4+-N contents of the wastewater produced in summer and autumn were lower than those of wastewater produced in spring and winter, but the TP contents of wastewater sampled in summer and autumn were higher than those sampled in spring and winter. The pollutant contents of the wastewater from swine farms with manual dry-collection system were relatively low, and the C/N ratio was high with biodegradability, therefore, the wastewater could be treated using biological methods.2. Experiments were conducted to investigate the effects of MBR on treatment of wastewater from swine farms with manual dry-collection system, 3 levels of hydraulic detention time 0.75、1.5、3.0d), dissolved oxygen(<1.5、1.5~3、>3mg/L) and reflux rate(200%、300%、400%) were used to form 9 combined experimental conditions(i. e. treatments) by orthogonal design. And the experiments were implemented in 3 batches, each batch of experments lasted for 50 d(Acclimatization period of 20 d and trial period of 30 d). when the average concentration of COD, NH4+-N, total nitrogen(TN) and total phosphorus(TP) in the influent waste-water were(3277±1192)mg/L, NH4+-N concentration was(203.8±51.2)mg/L, the average of total nitrogen(TN) was(361.0±133.3)mg/L, and the mean concentration of TP was(65.0±23.1)mg/L. the COD, NH4+-N, TN and TP contents of effluent were(202±201)mg/L,(56.6±54.0)mg/L,(91.6±69.1)mg/L and(19.2±10.0) mg/L respectively, and the corresponding removal rates were(94.3±5.8)%,(70.0±27.2)%,(70.7±20.7)% and(68.3±17.4)%. The removal rate of fecal coliforms was(99.9±0.08)%, and the amount of fecal coliforms in effluents samples ranged from 30 to 19350 count/L, 86.4% of the effluent samples could meet the requirements of national hygiene standard. The operational condition was optimized through range analysis of orthogonal tests, and the optimal condition was the treatment 4 with DO of 1.5~3.0mg/L, HRT of 3.0d and RR of 300%. Under such experimental condition, the COD, NH4+-N,TP concentrations of the effluent were(69.3±48.7) mg/L,(10.0±8.2)mg/Land(14.0±9.9) mg/L, respectively, and the corresponding removal rates were(97.8±1.5)%,(93.8±5.0)% and(81.5±14.2)%, respectively. The chromaticity of effluent of MBR is 80-90 degrees, and the corresponding transmission rate is12.1%-45.5% with 97% of ultraviolet sterilization rate.The effluent from MBR could be disinfected using ultraviolet to ensure biosecurity if the disinfected effluent was recycled for on farm flushing, which implicates the water resource conservation in swine production.3. If swine farm intended to discharge the MBR effluent, the phosphorate in the effluent must be further removed. Over 77.4% of the phosphorate in the MBR effluent was in the form of orthophosphate, therefore it could be easily removed using chemical methods. In order to meet the emission standards, Dosage of calcium hydroxide is 9mg/L, PAC is 6mg/L, iron sulfate is 6.5mg/L. Calcium hydroxide is the cost-effective reagent for phosphorate removal from MBR effluent according to removal effects of different reagents and their costs.4. Based on the above MBR experimental results and considering the operational cost of MBR, a pilot experimental system with capacity of 10m3/d was designed, which might be good reference for the further study of MBR for treatment of wastewater from swine farms.