Thesis for Doctor of Philosophy

Gilda de Sousa Carvalho
“Integrated treatment of textile industry wastewater in biological systems”
Ph.D. Biotechnology, IST, 2001
Supervisor: H.M. Pinheiro

Abstract

Textile industry wastewaters are characterised by high colour and organic matter concentrations, and wide variations in flow and composition. In this thesis, an integrated treatment process, consisting of a physico-chemical pre-treatment and an activated sludge system, was studied for its ability to remove colour and surfactants. A simulated cotton processing wastewater was estimated and characterised in terms of COD, N and P. This wastewater was used to evaluate the interference of common textile wastewater components in colour removal using chemical coagulation. An experimental set-up consisting of a sequencing batch reactor associated to a closed respirometer was selected among other tested hypotheses to perform biotreatability tests in activated sludge. Sludge response to shock loads and starvation periods was investigated, focused on surfactant-containing products, which represent a major COD fraction in textile wastewaters. Sludge acclimatisation and loss of adaptation to surfactants were analysed using TOC, surfactant concentration and respirometric data. A dynamic model was developed for surfactant biodegradation. The model parameter values were analysed to create sub-models able to describe the sludge acclimatisation process. Using the composed model, an optimal operation scheme was proposed to pre-acclimatise activated sludge before a surfactant replacement occurs in the textile process.

Keywords: textile wastewater; activated sludge; surfactants; respirometry; acclimatisation; modelling