Abstract
The paper presents the results of an experimental process designed for the treatment of the sewage generated by a rural community located in the north-east of Brazil. The process consists of a preliminary mechanical treatment adopting coarse screens and grit traps, followed by a biological treatment in a UASB reactor and a sub-surface horizontal flow phytodepuration step. The use of a UASB reactor equipped with a top cover, as well as of the phytodepuration process employing a porous medium, showed to present important health advantages. In particular, there were no significant odor emissions and there was no evidence of the proliferation of insects and other disease vectors. The plant achieved the following mean abatement efficiencies: 92.9% for BOD5, 79.2% for COD and 94% for Suspended Solids. With regard to fecal indicators average efficiencies of 98.8% for fecal coliforms and 97.9% for fecal enterococci were achieved. The UASB reactor showed an important role in achieving this result. The research was also aimed at evaluating the optimal operating conditions for the UASB reactor in terms of hydraulic load and organic volumetric loading. The achieved results hence indicated that the process may be highly effective for small rural communities in tropical and sub-tropical areas.
Highlights
The treatment of the domestic wastewater generated by small communities may be achieved applying various types of biological processes
The study was aimed at verifying the efficiency of the whole treatment process and of the individual treatment stages with respect to BOD5, COD, Suspended Solids (SS), settleable solids and two of the main microbiological indicators
The plant did not produce odors, thereby demonstrating the effectiveness of the top cover of the UASB reactor and the sub-surface flow adopted in the phytodepuration step
Summary
The treatment of the domestic wastewater generated by small communities may be achieved applying various types of biological processes. The efficiency of conventional processes (i.e., based on extended aeration activated sludge and trickling filters) is significantly affected by fluctuations of either sewage quality or flow rate, which are generally higher the smaller the size of the community. The effects of these fluctuations on the loss in efficiency of the treatment process has been reported in several studies (e.g., [1,2]). This problem can be overcome with the use of natural biological processes characterized by high retention times, such as lagoons and constructed wetlands. Since the early 90’s, solutions based on Up-flow
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