MAP Precipitation Recycling Of N And P From Swine Wastewater And Its Impacts On Traditional Anaerobic And Aerobic Processes

Swine wastewater is one of the major agricultural non-point source pollutants. In China, the treatment technology must meet the environmental protection standards. However, the existing processes of the treatments only aim to degrade or remove the NH4+-N and PO43--P without their recycling. This research utilized the new technique, MAP precipitation, as the pretreatment of the raw swine wastewater to precipitate the NH4+-N and PO43--P with MgNH4PO4·6H2O as struvite being a slow release fertilizer. In order to know the detailed influence on the subsequent process, various pollutants such as NH4+-N, PO43--P, COD, TOC and TC were monitored in the CSTR-SBR system with and without the MAP pretreatment. The results showed it is feasible to pretreat the swine wastewater with MAP technique, in which the NH4+-N and PO43--P were recycled. It improves the quality and quantity of biogas generation, and also the finally draining effluents easily meet the Chinese wastewater discharge standards. This paper offers a new idea in swine wastewater treatment. The main achievements in this research are as follows:1. The MAP technique can effectively lower down the NH4+-N and PO43--P concentrations in the supernatant of the swine wastewater after the precipitation; the removal efficiency of NH4+-N and the residual PO43--P were84.7%and1.35mg/L, and furtherly the COD, TOC and TC were also removed partly, the removal efficiency were22.3%,18.5%,23.1%, respectively, and the removal efficiency of SS all beyond80%seemed not to be influenced by the chemical dosage, the MAP contents MgNH4PO4·6H2O were maximum81.5%at pH9.0as tested by the XRD.2. The batch experiment in bottles of anaerobic fermentation was carried out after the MAP precipitation pretreatment. The results showed that NH4+-N concentration can be effectively controlled in the supernatants in the anaerobic process.the C/N ratio was enhanced from2.8to6.6. The amount of TOC remained130mg/L lesser than in the raw wastewater; while COD, TOC and TC degraded11.7%,4%and8%more than that in the raw wastewater, respectively. So, better performance of anaerobic treatment was gas yield rate and methane production at0.307L/(g-VS) against0.295L-CH4/(g-VS) higher than in the raw wastewater. The dynamics of anaerobic treatment with CSTR technology was studied in the supernatant and the raw swine wastewater. There was better performance in the supernatant and2or3days in advance in the supernatant at the same level degradation. The volume loading rate of the supernatant increased to2.2kg-COD/m3-d, but only1.5kg-COD/m3-d of the volume loading rate to the raw wastewater. At the same time, the gas rate between the supernatant and the raw were0.462and0.393m3/kg-COD, and the CH4contents were67.9and61.5%, respectively.3. Aerobic SBR technology was chosen for subsequent treatment of the effluents from the anaerobic digesters, the average removal efficiencies of COD, NH/-N and PO43--P of the effluents with and without pretreatment of MAP technique were82.8%,95.3%,94%and75.5%,74.5%,62%, respectively. The concentrations of NO2--N and NO3--N in the effluent of supernatants were48.6mg/L and8.6mg/L4. When the CSTR and SBR technology were combined together, the concentrations of NH4+-N, PO43--P and COD from the effluents of the supernatants pretreated with MAP technique were13.5,1.3and258mg/L, respectively, which met the Chinese discharge standard (GBI8596-2001).These values were256.1,25.67and424.4mg/L in the raw wastewater without MAP technique.