Effect Of Adding Wheat Straw On The Low Strength Wastewater In The Two-Phase Anaerobic Treatment

At present, the low-strength wastewater is mainly treated by activated sludge process, contact oxidation, biological filter, and so on. But the aerobic process has some weak points, such as high energy consumption, larger working area, complex management, and so on. since the anaerobic biological treatment technology is becoming more and more mature, many scholars began to study anaerobic process for low-strength wastewater treatment, however, the organic content in the low-strength wastewater is low, and it can not provide sufficient nutrients for the microbes, which could easily lead to the issues of ineffective treatment and energy waste, moreover, the biogas production of low strength wastewater treated by anaerobic process is small.In the rural areas of china, all of the sewage and garbage are almost directly discharged without treatment, so this paper is to find an innovative management model of the sewage and waste—The sewage/garbage integrated treatment mode, namely in the course of two-phase anaerobic treatment of low strength wastewater, the author adds wheat straw into the acidogenic phase to improve its effluent concentration of organic matter, thereby improving the handling effectiveness and gas production of the methanogenic phase. The author studies the impact of pH, HRT, wheat straw dosing ratio and wheat straw repeated dosing on the acidogenic phase, and the impact of HRT on the methanogenic phase.The research results show that:in the different pH conditions, acidic conditions can not only improve the effluent VFA concentration and acidification effects, but also can enhance the effects of acid bacteria on the decomposition of wheat straw, and in the acidogenic reactor, the effluent COD concentration of the first cycle is significantly higher than that of the remaining cycles;In the different HRT conditions, HRT increasing from 3h to 8h, it does not have great effect on the pH environment of the acidogenic phase, nor will remain a high level of the effluent COD concentration in the acidogenic phase, it slows down the decreasing rate of the effluent COD concentration only, but it will increase the effluent ammonia concentration of the first few cycles in the acidogenic phase; In the different dosing ratios conditions, the used wheat straw dosing ratio as 1:2,1:1.5 and 1:1, does not cause a big impact on the acid environment, the maximum effluent COD concentration of the first cycle is 1744 mg·L-1,1382 mg·L-1,981 mg·L-1, respectively in the acidogenic reactor, the ratio of the maximum COD concentrations is 1.8:1.4:1, which is basically consistent with the dosing ratio-2:1.5:1, so it shows that the increase of dosing ratio is regular along with the increase of the effluent COD concentration, and the increase of wheat straw dosing ratio will correspondingly increase the effluent VFA concentration, acidification rate and ammonia concentration in acidogenic reactor; The application of repeated dosing ways can slightly increase effluent pH of the acidogenic phase, and it can also maintain a high organic matter concentration of the effluent in the acidogenic phase, such as the average effluent COD concentration is 867 mg·L-1 in the repeated dosing reactor, while the average effluent COD concentration is 364 mg·L-1 in the one-time dosing reactor. Equally compared with one-time dosing, the repeated dosing way can increase effluent ammonia concentration, VFA concentration and acidification effects. In the different HRT conditions, the effluent pH does not have any significant changes in the methanogenic phase, but the effluent ammonia concentration is always greater than the influent ammonia concentration, therefore, it must be taken into account the effect of increase of ammonia concentration on the production of methane bacteria. With HRT at 4h, the COD removal is lower in the methanogenic phase, and with HRT at 12h, which is the highest, though the HRT extends from 6h to 14h, the increase of COD removal rate is not great. The changing trend of the VFA and methane gas production rates also show that when the HRT is at 14h, their average effluent VFA concentration is still 198 mg·L-1, while with the HRT at 4h,6h and 9h, the gas production rate hardly changes, so it can be seen that to extend the HRT has limited impact on the upgrading ability of wheat straw-containing waste water treatment in the methanogenic phase.