Integrated sewage treatment system (ISTY) is a new technology for rural domestic sewage treatment. In the ISTY, the carbon source in the denitrification stage is often insufficient, affecting the denitrification efficiency. In order to improve the denitrification efficiency, several commonly available agricultural wastes, peanut shell (PS), sawdust (SD), peat (PT), and their mixtures (MT), were selected as supplementary carbon sources in the denitrification stage of ISTY to study the denitrification efficiency. Results show that PS exhibited a high carbon release capacity. PS released an enormous amount of carbon in 144 h, and the cumulative total organic carbon was 41.99 ± 0.7 mg/(g·L). The optimum carbon source dosage was 3 g/L, the nitrate removal rates of PS exceeded 95% after 48 h, and the denitrification rates were 9.35 mg/(g·L), which were 63.92% higher than that of the control group. After running the ISTY for 120 h, and with PS as supplementary carbon sources, the removal rate of TN increased from 29.76% to 83.86%. At the genus level, the dominant denitrifying bacteria in ISTY, after adding PS, were Pseudomonas and Cupriavidus, accounting for 78.68%, an increase of 72.90% compared with the control group. This evidence suggested that PS can obviously enhance the denitrification efficiency of the ISTY as a supplementary carbon source.
In rural toilets, black water still remains polluted by nitrogen and phosphorus after being pre-treated by septic tanks. This study uses aerated biofilters to purify black water, screen the biofilter filler, and determine its effect on nitrogen and phosphorus purification in rural black water. This study introduced the concept of the “shape factor” into the Langmuir and Freundlich equations and optimized the isotherm adsorption model to better fit the actual dynamics of nitrogen and purification in black water. Combined with the first-order kinetic equation, the double constant equation, and the Elovich equation, the adsorption performance of seven kinds of biofilter fillers (i.e., zeolite, volcanic rock, sepiolite, ceramsite, anthracite, vermiculite, and peat) was studied. Then, the biofilter was constructed using a combination of fillers with better adsorption properties, and its ability to purify rural black water was studied. Results showed that vermiculite and zeolite had little effect on nitrogen and a high saturated adsorption of 654.50 and 300.89 mg·kg−1, respectively; peat and ceramsite had little effect on phosphorus and a high saturated adsorption of 282.41 mg·kg−1 and 233.89 mg·kg−1, respectively. The adsorption rate of nitrogen from fast to slow was vermiculite > peat > zeolite > volcanic rock > sepiolite > ceramsite > anthracite. The adsorption rate of phosphorus from fast to slow was peat > ceramsite > zeolite > sepiolite > vermiculite > volcanic rock > anthracite. Four combined biological filter fillers aided the removal of nitrogen and phosphorus from rural high-concentration black water. The combination of zeolite and ceramsite filler had a good nitrogen and phosphorus removal effect in high-concentration black water. After the system was stable, the nitrogen removal rate attained 71–73%, and the phosphorus removal rate attained 73–76% under the influent condition of total nitrogen and phosphorus concentrations of 150–162 and 10–14 mg·L−1, respectively. This study provides technical support and reference for the purification and treatment of rural black water.
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