Coupling Of Sequencing Batch Reactor And UASB Reactor For Piggery Wastewater Treatment At Ambient Temperature

With the optimization of agricultural distribution and adjustment of the industrial structure, intensive poultry and livestock operations have been rapidly developed. It has greatly boosted the people’s living standards, however, the environmental problems brought by the livestock and poultry farms are becoming more serious. In this paper, it analysed the source, characteristic and harm of the piggery wastewater, and summarized the piggery wastewater treatment methods at home and abroad, and it also contrasted the treatment results and economic rationalization and considered the characteristic of the piggery wastewater, which containing high organic, high ammonia nitrogen and high suspended substance. Based on this, it proposed a solution that adopted UASB reactor coupling of sequencing batch reactor to treat piggery wastewater at ambient temperature. The experiment conditions corresponded with practical engineering. We especially examined the startup process of UASB reactor and operation conditions, and studied the treatment effect of SBR reactor at two different operation cycle. It had certain guiding significance to the practical engineering. The results showed that:1. The startup process of UASB reactor experienced186days by using piggery wastewater as intake water, which was made simply solid-liquid separation, and adopting the way of intermittent water intake at changing ambient temperature. The entire startup process divided into sludge acclimation stage, improving loading stage, stable operation stage and low-temperature operation stage, which respectively operated90days,56days,18days and22days.2. In the whole startup process of UASB reactor, the environment temperature ranged between19℃and32℃. The pH value range of influent and effluent was6.20～8.61and6.20～8.61respectively, without apparent acidification phenomenon. The concentration ranges of chemical oxygen demand (COD), total phosphorus(TP), and suspended solids(SS) of influent were1,467～9,035mg/L,27.30～152.77mg/L,490～3,770mg/L, respectively. The concentration ranges of chemical oxygen demand (COD), total phosphorus(TP), and suspended solids(SS) of effluent were445～4,186mg/L,13.89～142.58mg/L,120～1,470mg/L, respectively. It had no effect on ammonia nitrogen(NH3-N) removal, and the concentration ranges of ammonia nitrogen(NH3-N) of influent and effluent was very similar, which was respectively93.73～919.03mg/L and171.24～873.62mg/L.3. As to the organic loading rates(OLRs) of UASB reactor, it had a rising trend earlier, and later fell a little by low temperature. The OLRs ranged between0.16kgCOD/(m3·d) and5.74kgCOD/(m3·d). With organic loading rates increasing, hydraulic retention time(HRTs) gradually shortened from9.2days to0.9day.4. During the sludge-acclimation stage, OLRs gradually increased from0.27--0.47kgCOD/(m3·d) to1.60～2.10kgCOD/(m3-d). During the improving-loading stage, at beginning OLRs was about1.54kgCOD/(m3·d), and the COD removal efficiency was about80.43%; on the111th day OLRs increased to1.94kgCOD/(m3-d), and the COD removal efficiency was about90.14%; on the145th day OLRs increased to5.68kgCOD/(m3·d), and the COD removal efficiency decreased a little, which was about73.34%. HRTs gradually shortened from3.5days to1.1days. During the stable-operation stage, the average OLRs was4.16kgCOD/(m3·d) when the average temperature was17℃, and the average COD removal efficiency was76.98%, and the HRTs was about1day. During the winter, the average temperature was11℃, and the low temperature had bad results on the treatment effect. The average OLRs was3.16kgCOD/(m3·d). and the average COD removal efficiency was68.95%, and the HRTs was about1.5days.5. At the end of the startup process, it successfully cultured anaerobic granular sludge with excellence subsidence performance. The average particle size of granular sludge was1.03mm, and the maximum size was about4mm. The wet density was about1.02g/cm3. The settling velocity was between65.45and144.00m/h, and the average settling velocity was100.24m/h. As the particle size of granular sludge increased, the settling velocity of granular sludge was increased. They were positively related, and the fitting equation is y=19.663x+54.384, and correlation coefficient R2=0.9739. TSS and VSS of anaerobic sludge was65.87g/L and32.51g/L, and VSS/TSS was49.35%. By scanning electron microscope (SEM) to observe the surface of granular sludge, it found that the granular sludge was inerratic, approximately spherical appearance, and the surface was uneven and had more cavities.6. As to net biogas yield and biogas yield ratio, it also had a rising trend earlier, and later fell a little by low temperature. The net biogas yield ranged between0.01L/d and15.12L/d. The biogas yield ratio ranged between0.01m3(kgCOD·d) and0.44m3/(kgCOD·d). It had difference to the theoretical value.7. The SBR experiment experienced about117days. It divided into two stages, which the operation cycles were24h and12h, respectively. During24h operation cycle, the environmental temperature was about27℃, and the effluent quality could basically meet the demand of Discharge Standard of Pollutants for Livestock and Poultry Breeding, but the operation cycle time was slightly longer. During12h operation cycle, the environmental temperature was under15℃, which had a serious effect on the activities of microorganisms. The effluent quality became poor. At the same time, to get good removal efficiency of nitrogen and phosphorus, it needed to discharge the sludge regularly, and it recommended that the discharge time interval ranged between20days and25days, and it also needed to control amount of sludge which would be discharged.8. The entire UASB-SBR joint system experienced about117days. Through the analysis of treatment effect of UASB-SBR joint system, it found that the process could get approving results treating piggery wastewater at ambient temperature when the temperature was above15℃, and the results could basically achieve the requires of Discharge Standard of Pollutants for Livestock and Poultry Breeding in China. However, when the environment temperature droped to about10℃, the effluent quality got worse, because it had serious effects on microbial activity at the low temperature in winter.