Green pit technology as a rural sanitation component for the semiarid region of Brazil

ABSTRACT The green pit module corresponds to an alternative model to treat domestic sewage in rural areas, which considers water reuse in productive yards, contributing to rural sanitation. The present investigation has assessed the green pit module performance based on 70 modules installed in the semiarid region of Brazil and includes sanitary quality test of cultivated vegetables, sizing proposal, rate of accumulation of the sludge produced and evaluation of the maintenance period of the green pit module. A design method was presented, which is based on water consumption, and has been assessed on site for two kinds of homes: those with (R1) and without (R2) tap water supply. In addition, we measured the sewage contribution and return coefficient for each case. The analyzed samples of tomato (Solanum esculentum), pepper (Capsicum chinense), banana (Musa sp.) and “malvarisco” leaves (Plectranthus amboinicus L.) presented low levels of coliform (below ten colony-forming units per gram) and absence of Salmonella sp., which complies with the Brazilian sanitation legislation. The water consumption for R1 and R2 were 50 and 34 L.resident-1.day-1, whereas sewage per capita production totaled 13.1 and 1.2 L.resident-1.day-1 for R1 and R2, respectively. This indicates return coefficients of 26 and 3% for R1 and R2, respectively, which differs significantly from the usually recommended value (80%). The system presents low maintenance demand: the sludge should be removed every 5.3 years, on average.

摘要 绿池模块（green pit module）是一种农村生活污水处理的替代模式，其将生产性场地的水资源回用纳入设计考量，有助于推动农村卫生事业发展。本研究依托巴西半干旱地区布设的70套绿池模块，对其处理性能开展系统性评估，评估范围涵盖种植蔬菜的卫生质量检测、模块选型设计方案、所产污泥的累积速率以及绿池模块的维护周期评价。本研究提出了一种基于用水量的设计方法，并针对两类家庭开展现场验证：配备自来水供水的R1类家庭与未配备自来水供水的R2类家庭；此外，本研究还分别测定了两类场景的污水贡献量与回用系数。本次分析的样本包括番茄（Solanum esculentum）、辣椒（Capsicum chinense）、香蕉（Musa sp.）以及马瓦里斯科（Plectranthus amboinicus L.）叶片，检测结果显示其大肠菌群水平较低（每克样品中菌落形成单位低于10个），且未检出沙门氏菌属（Salmonella sp.），符合巴西卫生法规要求。R1类与R2类家庭的人均日用水量分别为50升·人⁻¹·天⁻¹与34升·人⁻¹·天⁻¹，而两类家庭的人均日污水产生量则分别为13.1升·人⁻¹·天⁻¹与1.2升·人⁻¹·天⁻¹；据此计算得到R1与R2类家庭的污水回用系数分别为26%与3%，这与通常推荐的80%回用系数存在显著差异。该系统维护需求较低，平均每5.3年需清理一次污泥。