农村生活 污水 在 村落 尺度上 排放较为分散 、 排 水量较小且水量时空变化波动大 。 长期以来 我国 农村排水 管道 设计 主要 是依据城市排水管道 设计规范， 其结果是 管径 偏大 ，导致 管网投资高， 而且 污水 在管道中停留时间长，出现沉淀和厌氧反应，存在 安全隐患。 小管径排水系统可以 在保证污水收集率的同时 显著降低管道敷设费用 但目前有关小管径排水系统的研究 很 少 。本 研究以 农村小管径排水 管道 为对象， 解析 管道内微生物 的 生长、 污染物 转化 及 有害气体产生规律 及 特征 ，提出农村小管径排水系统的管道优化设计方案，为 适合农村地区的小管径排水系统的构建 提 供科学依据 。搭建了小管径排水管道的模拟平台，根据农村地区排水特征，设计了2 种流态（定常流 、 时变流） 和 3 种坡度（ 5 10‰ 15 实验 方案， 研究 了不同水质（生活污水、灰水） 情况下 管道内微生物 生长与 物质转化 特点 ，结果如下
1 生活污水 管道 与灰水管道 微生物的生长和演替特征不同 。 两种管道生物膜的厚度变化规律类似，但生物膜形貌及 胞外聚合物 组成差异明显。 生活污水管道生物膜细菌数 及 悬浮细菌数 均明显高于灰水管道且两种管道内 细菌 属水平差异很大，演替规律不同 。 水体溶解氧 DO 浓度和管道长度对于管道生物膜细菌群落 演替的 影响有限。 生活污水和灰水 管道生物膜上 具有反硝化功能的细菌Denitrifying bacteria, DNB 数 >硫酸盐还原 细 菌（ Sulfate-reducing bacteria, SRB数 >产甲烷 古 菌（ Methanogenic archaea, MA 数 且 因 SRB和 MA的 竞争关系导致 MA被逐渐淘汰 生活污水管道生物膜中 DNB、 SRB和 MA的数量均比灰水管道生物膜高 1 2个数量级 。 灰水 及其 管道生物膜中 水源性 致病菌 Water-related pathogenic bacteria, WPB 的数量明显低于污水管道，生物安全性相对较 高 。
2 生活污水管道与灰水管道内污染物转化规律不同。 两种管道均具有明显的 COD去除能力，但 TN去除能力有限且均无NH4+-N和 TP去除能力 。 生活污水管道 内 硫化物 和甲烷转化过程 与管道生物膜中 SRB和 MA的演替规律一致管道运行前 30天产甲烷明显而基本无硫化物产生， 60天后 管道 硫化物产量较高而甲烷产量下降 污水硫化物 浓度 随 管道停留时间的增大而 明显 升高 。 灰水管道硫化物产量很低 管道 H2S浓度 仅为污水管道的 4分之一 且 基本不含 CH4 这种差异主要是由于两种管道中 SRB和 MA的数量差距 、 管道 DO环境的不同 以及水体本底 H2S和 CH4浓度差异 导致的，与水体中 乙酸、丙酸等挥发性脂肪酸浓度以及硫酸盐浓度 基本无关。
3 农村排水量的周期性变化和管道坡度的差异显著影响小管径排水管道生物膜的细菌群落特征。污水流量的周期性变化和大坡度（ 的管道敷设方案可以 有效 降低污水管道生物膜上 SRB的相对丰度，对于管道 SRB削减和管道H2S控制有利 。 灰水流量的周期性变化可以显著降低灰水管道生物膜上 WPB的相对丰度，大坡度（ 的管道敷设方案有助于降低生物膜中 Legionella 军团菌属 的相对丰度 充分利用灰水水量的变化并采用大坡度的管道对于灰水管道生物膜中 WPB的控制有利。
基于上述研究结果，建议农村 小管径排水管道收集混合生活污水时应注意管道 H2S的积累问 题， 应科学设置通风设施 、 减少水量调节设施并适当加大管道坡度，协同减少管道 H2S积累 。 农村 小管径排水管道单独收集灰水不须额外建设通风设施，且其 COD去除能力对于实现灰水达标排放或灌溉回用具有一定的正面效应 。 可以采取多种技术和管理手段降低管道堵塞和恶臭的发生率， 提高农村小管径排水管道的长期运行稳定性和安全性。
Rural domestic sewage displaces less and discharges more widely at the village scale, and the sewage quantity fluctuates greatly. The rural sewer design is mainly based on urban sewer regulation for a long time, causing large sewer diameter, high cost, and long sewage retention time which could cause doposition and anaerobic bioreaction and cause safety risks. Small diameter sewer (SDS) can ensure the sewage collection rate and significantly reduce the cost, but the research of SDS is little till now. In this study, SDS was taken as the object to analyze the regulation and characteristics of sewer microorganism growth, pollutants transformation and harmful gases generation. The optimal design of SDS was proposed to provide a scientific basis for SDS build in rural areas.
The simulation platform of SDS was built. Two kinds of flow conditions (stable and variable) and three slopes (5‰, 10‰, 15‰) were designed according to the drainage characteristic of rural areas. The characteristics of sewer microorganism growth and substance transformation were studied with two kinds of wastewater (domestic sewage and greywater). The results are as follows:
1) The characteristics of microorganism growth and succession were different in domestic sewage and greywater sewers. The biofilm thickness regulations of two kinds of sewers were similar but the biofilm morphology and extracellular polymeric substance composition showed obvious distinction. The biofilm and suspended bacteria number of the sewage sewers were higher than the greywater sewer and the bacterial genus level distinction and succession were obviously different. The effect of dissolved oxygen (DO) concentration and sewer length on biofilm bacterial community succession was limited. The number of denitrifying bacteria (DNB) > sulfate-reducing bacteria (SRB) > methanogenic archaea (MA) in sewage sewer biofilms and greywater sewer biofilms and MA were gradually eliminated due to the competitive relationship between SRB and MA. The number of DNB, SRB and MA in sewage sewer biofilms was 1-2 orders of magnitude higher than that in greywater sewer biofilms. The number of water-related pathogenic bacteria (WPB) in greywater and greywater sewer was obviously lower than that in sewage sewer, which meant greywater sewer had relatively higher bio-safety.
2) The pollutant transformation in domestic sewage and greywater sewers was different. Two kinds of sewers both had obvious removal capacities of COD, but the removal capatites of TN were limited. They didn’t have the removal capacity of NH4+-N or TP. The transformation of sulfide and methane in sewage sewer was corresponded with the succession characteristic of SRB and MA in sewer biofilms. Methane generation was obvious but basically no sulfide was generated in the first 30 d while after 60 d the sulfide generation was high and methane production went down. Sulfide concentration increased obviously during sewage retention time. The sulfide generation in greywater sewers was low. H2S generation was only one fourth of that in sewage sewers and CH4 was almost not contained in greywater sewers. These were mainly caused by the difference of SRB and MA number, the DO condition, and the background concentration of H2S and CH4, which was basically independent of the concentration of VFAs (including acetic acid, and propionic acid etc.) and sulfate.
3) Periodic changes in rural drainage and sewer slopes caused significant influences on the characteristic of bacterial communities in SDS biofilms. The periodic variation of sewage flow and high slope (15‰) scheme could effectively reduce the relative abundance of SRB in sewer biofilms, contributing to SRB and H2S reduction in sewers. The periodic variation of greywater flow could significantly reduce the relative abundance of WPB in sewer biofilms. High slope (15‰) scheme was conducive to the reduction of Legionella relative abundance. Making full use of the changes of greywater flow and high sewer slopes was beneficial for biofilm WPB control.
Based on the above results, H2S generation should be focused on sewage SDS and methods such as scientificly setting ventilation facilities, reducing adjusting facilities, and taking high slopes should be taken to reduce the H2S generation jointly. It is not necessary to bulid extra ventilation facilities in greywater SDS and the COD removal of greywater SDS has certain positive effects on greywater discharge in compliance with regulations and reuse to irrigation. Varieties of techniques and management measures can be used to reduce the incidence of sewer blockage and odor to improve the long run operation stability and safety of SDS.