The Influence Of The Separation Of Wastewater Into High Content Liquid And Low Content Liquid On Combined Anaerobic- Aerobic Process

Animal waste has become an important source of environmental pollution, with the wastewater from swine breeding accounting for the largest. It is an urgent need to find a cost-effective, reliable treatment method. At present, there are mainly two problems in the treatment of swine wastewater. The first problem is that the biogas production efficiency is low due to the large volume of wastewater resulting in hard to increase temperature. The second problem is that the digested effluent cannot be fully utilized, and the performance of aerobic post-treatment of digested effluent is poor. Aiming at these problems, on the basis of early research, this paper studied the subject of "the influence of the separation of wastewater into high content liquid and low content liquid on combined anaerobic- aerobic process ". The results are listed as follows:(1) A full-scale experiment of solid-liquid separation was carried out in the plant of swine wastewater treatment. The results showed that after solid-liquid separation, the removal rates of COD, BOD5, TS, SS, TKN and TP from raw wastewater were 10.03%, 19.23%, 6.90%, 10.08%, 14.14%, 14.42%, respectively, and almost no NH3-N was removed. The solid–liquid separation had no significant effect on the post-separation of low content liquid and high content liquid. The separated slurry can be further separated to high content liquid and low content liquid, with a good separation performance.(2) The influence of volume separation ratio on the post-separation was also be tested. The result showed that through separation by means of gravity sedimentation, the volumes and mass of swine wastewater were distributed in an unbalanced form. Most pollutants and nutrients were separated into high content liquid with a small volume. With volume ratio of the high content liquid increased, the pollutants in it increased too, decreased in low content liquid correspondingly. Although the volumes of high content liquid accounted for only 10%–30% of the total volume of raw wastewater, their methane output accounted for 63.38%–76.61% of the total methane output of raw wastewater.(3) The separation ratio also influenced the performance of the aerobic unit. S2(2:8) system achieved the best performance in aerobic treatment of mixed liquid of low content liquid and digested effluent of high content liquid. The COD removal rate was 85.4%, with an effluent of 256 mg/L. The NH3-N removal was above 99%, with an effluent of below 5 mg/L. The pH value of mixed liquid in SBR at the end of aeration was stable at more than 7.0. The performance of the aerobic unit of S1(1:9) followed that of S2(2:8). S3(3:7) system had the poorest performance. COD removal rate was only 56.9%, with an effluent COD concentration ≥946 mg/L, and NH3-N removal rate was about 95.0%, with an effluent concentration ≥30 mg/L. The pH value of mixed liquid in SBR at the end of aeration was unstable and below 7.0. Considering the efficiency of biogas fermentation in anaerobic unit and the removal results of pollutants aerobic unit, a volume ratio of 2:8 of high content liquid to low content liquid was the most suitable separation ratio.(4) Further treatment to the SBR effluent was tested. The flocculation process was superior to the oxidation treatment. The best flocculants combination was Cao+PAM, with the final concentration of 800 mg/L for Cao and 2mg/L for PAM. In this situation, the effluent of flocculation could reach 83 mg/L for COD, 7.36 mg/L for NH3-N, 0.3 mg/L for TP, 16 times for chromaticity, meeting the standard of discharge standard. The cost was 0.475 yuan/t wastewater.(5) The technology and economic analysis for combined anaerobic-aerobic process based on separation of wastewater into high content liquid and low content liquid was conducted. The combined anaerobic-aerobic process based on separation and Anarwia process performed quite the same and significantly superior to the traditional combined anaerobic-aerobic process. At the same time, the combined anaerobic-aerobic process based on separation improved the efficiency of biogas production, with the volumetric biogas production rate increasing by 282% than traditional combined anaerobic-aerobic process and Anarwia process. Although the costs of the combined anaerobic-aerobic process based on separation and Anarwia process were similar, the volume of anaerobic unit of the former decreased by 72.36%, and saved 23.27% of the total investment cost.Generally, the combined anaerobic-aerobic process based on separation could not only improve the efficiency of biogas production, but also solved the problem of poor performance in aerobic post-treatment of digested effluent. So it is a more cost effective and reliable process than the conventional anaerobic-aerobic process and Anarwia process.