Characterization and clarification by sedimentation of the backwash water from rapid sand filters of a water treatment plant which uses ferric choride as primary coagulant

Author(s)

Aloysio Gomes de Souza Filho

• Document type: Master's Dissertation
• Press: São Carlos.
• Institution: Universidade de São Paulo (USP). Escola de Engenharia de São Carlos (EESC/SBD)
• Defense date: 1998-03-27

Examining board members

Luiz di Bernardo; João Sérgio Cordeiro; Sidney Seckler Ferreira Filho

• Advisor: Luiz di Bernardo

Abstract

The water treatment plants produce wastewater during the treatment process, resulting mainly from filter backwashing which can amount to 5 of the treated water. The common practice has benn to discharge these wastes into the nearest water bodies or into the urban drainage network. It is necessary to conduct studies to minimize the washwater volume and also provide for its treatment in order to obtain adequate final disposal of such waters for each plant. The reuse of the backwash after due clarification process is important as it contributes to meeting rising water demands and the reduction fo waste waters. This study emphasised the characterization and clarification of filter backwash which employs ferric cloride as the pimary coagulant making experiments in sedimentation column. Through these experiments it was found that the supematant obtained using cationic, anionic and nonionic polymers offered better qualities than that resulting from sedimentation without the use of these conditioners and even better than the raw water quality showing the feasibility of recycling. Anionic polymer was found to produce best results in the treatment of backwash. (AU)