Treatment of dichromate-based cod-analysis wastewater for chromium removal by sequential sulfite reduction and alkali precipitation

Date

4-2011

Degree

Bachelor of Science in Chemical Engineering

College

College of Engineering and Agro-Industrial Technology (CEAT)

Adviser/Committee Chair

Catalino G. Alfafara

Committee Member

Jerico R. Aguila, Maria Cristina V. Mahilum

Request Access

To request access of this material, please email the administrator at uscs-mainlib.uplb@up.edu.ph

Abstract

A combined sulfite reduction and alkali precipitation treatment strategy was employed to treat dichromate-based COD-analysis wastewater for hexavalent chromium removal. The sulfite reduction was to reduce the hexavalent chromium in the wastewater into its less toxic trivalent form, and alkali precipitation was to remove the trivalent chromium into chromium hydroxide sludge. The hexavalent chromium reduction efficiency was found to increase with increasing sulfite dose. The highest reduction efficiency achieved was 98.44%, corresponding to 10.55 mg/L of sodium sulfite added. Alkali precipitation experiments of the effluent after sulfite reduction (under the best reaction conditions) showed that the pH-point of minimum solubility was at 7.5, which was different from the theoretical value of pH 8.5. In addition, precipitation efficiency increased with pH (pH 6.5 to pH 10.5). The highest precipitation efficiency of 98.62% was observed at pH 7.5. The alkali dosage and amount of sludge produced after alkali precipitation were found to increase with increasing pH. At the point of minimum solubility (pH 7.5) the sludge formed and alkali dosage were 239.42 g/L and 256.67 g/L, respectively. The wastewater treated using the combined reduction-precipitation treatment strategy complied with the DAO No. 35 for Class C Standards in terms of pH and residual Cr(VI). The treatment cost of 1 cubic meter of wastewater was estimated at Php25.31 for sulfite reduction and Php42.09 for alkali precipitation.

Language

English

Location

UPLB College of Engineering and Agro-Industrial Technology (CEAT)

Document Type

Thesis

This document is currently not available here.

Share

COinS