秸秆过滤猪场废水及滤料与猪粪好氧堆肥研究

秸秆具有较大的比表面积，对猪场废水中悬浮固体及氮素等养分具有较好的截留及吸附特性，有助于猪场废水后续资源化利用，但过滤后秸秆滤料的高效再利用又成为新的研究热点。该研究利用玉米秸秆过滤猪场废水，研究过滤后的秸秆滤料与猪粪好氧堆肥效果，堆肥过程中碳、氮转化及有害气体的排放规律。结果表明：玉米秸秆过滤猪场废水最优工艺条件为：滤层容重为0.15 g/cm3，过滤管径为9 cm，装填高度为40 cm，此条件下猪场废水总氮（Total Nitrogen，TN）、总悬浮固体和化学需氧量的去除率分别为22.80%、51.60%和76.81%。在初始C/N、环境温度、含水率、通风速率分别为20～35、22.32～32.05 ℃、65%、0.2 m3/h条件下，初始C/N越高，堆肥效果越好，堆体总有机碳（Total Organic Carbon，TOC）损失越大，而TN损失越小，有害气体排放主要集中在堆肥前期；初始C/N为35时，最高堆体温度达65.96 ℃，高温期（>50 ℃）可维持21 d，其中60 ℃高温长达12 d，种子发芽指数和TOC、TN损失率分别为81.03%、57.73%和10.08%，虽然CH4、CO2排放有所增加，但NH3、N2O排放和氮素损失显著降低（P<0.05），CH4、CO2、N2O 3种温室气体的温室效应影响潜值为137.53 kg/t（以CO2为当量）。研究为秸秆滤料和猪粪的资源化利用及其好氧堆肥过程有害气体的减排提供基础依据。

Straw filtering wastewater and aerobic composting of filter residues and manure on a pig farm

Pig-farm wastewater is characterized by high suspended solids, organic matter, and ammonia nitrogen content. It is very difficult to treat, due mainly to the complex composition of the pig manure and feed residues. Fortunately, the straw with a large specific surface area can be expected to serve as the better retention and adsorption for the suspended solids and nutrients. For example, nitrogen content decrease can be greatly contributed to the subsequent resource utilization of pig-farm wastewater. However, it is still a new challenge for the efficient reutilization of straw filter residues. Alternatively, aerobic composting can be used to produce the organic fertilizer for better soil fertility and structure, due to the easy operation, short reaction period, better reduction, cost saving, and environmentally friendly. It is a promising way to simultaneously dispose of straw filter residues and pig manure in an intensive pig farm. Compared with the dry straw, the filtered straw is easily decomposed to participate in the composting process, where the high porosity can facilitate to absorb the water and swells. Meanwhile, the composting process is accompanied by the emissions of greenhouse gases and stenches, such as methane (CH4), carbon dioxide (CO2), nitrous oxide (N2O), and ammonia (NH3), due to the complex composition of pig manure. Moreover, the composting microorganisms can quickly utilize the ammonium nitrogen that is adsorbed by the straw in the process of filtration. But the ammonium nitrogen is also easily volatilized to produce the NH3 for secondary pollution, leading to the reduced quality of compost due to nitrogen loss. However, it is still unclear on the relevant composting characteristics of the straw filter residues mixed with the pig manure. This study aims to filter the pig farm wastewater through maize straw and then systematically investigate the aerobic composting of straw filter residues and pig manure, the conversion of carbon and nitrogen during composting, as well as the emission of harmful gases. The results showed that the optimal conditions for the maize straw filtering the pig farm wastewater were as follows. The bulk density and height of the maize straw filter layer were 0.15 g/cm3 and 40 cm, respectively, whereas, the inner diameter of the filter column was 9 cm. The removal rates of Total Nitrogen (TN), Total Suspended Solids (TSS), and Chemical Oxygen Demand (COD) in the pig farm wastewater were 22.80%, 51.60%, and 76.81%, respectively, under the optimum conditions. Furthermore, the higher the initial ratio of the carbon to nitrogen (C/N) was, the better the composting was, the more the Total Organic Carbon (TOC) loss was, and the less the TN loss was, when the initial C/N, ambient temperature, moisture content, and ventilation rate were 20-35, 22.32-32.05 ℃, 65%, and 0.2 m3/h, respectively. The harmful gas emissions mainly occurred in the early stage of composting. At the initial C/N of 35, the highest composting temperature reached 65.96 ℃ and the high-temperature period (>50℃) was maintained for 21 days. Among them, the maintenance time above 60 ℃ was up to 12 days. The seed germination index (GI), the loss ratio of TOC and TN after composting of 36 d reached 81.03%, 57.73%, and 10.08%, respectively. Although the emissions of CH4 and CO2 increased, there was a significant decrease in the emissions of NH3 and N2O, as well as the nitrogen loss during composting. The potential greenhouse effect was 137.53 kg/t (in CO2 equivalent) for the three greenhouse gases of CH4, CO2, and N2O. Therefore, the local anaerobic reaction can be avoided to reduce the generation of CH4 under high C/N conditions. The findings can provide the favorable support for the resource utilization of the straw filter residues and the emission reduction of harmful gases in the aerobic composting process of straw filter residues and pig manure.