Ceramic membrane technology applied to oily wastewater separation

Abstract

Hong Kong has also been working rigorously to improve its water quality since the 1980s. The implementation of the first stage of the Harbour Area Treatment Scheme (HATS) has resulted in great improvement in the water environment in Victoria Harbour which was one of the most seriously polluted areas in Hong Kong. According to the report of the Drainage Services Department (DSD) in 2003, the trade effluent surcharges collected from the restaurant industry reached as high as 72.4% of surcharges collected from all trade types. One of the main reasons was due to the ineffectively control of oil concentrations in wastewater under the existing oil-trap method. Membrane separation is becoming a promising technology for the 21st century. Membrane separation technology has several advantages such as stable effluent quality, no chemicals addition, small area occupied, a high volume concentration ratio achieved. The main work presented in this thesis includes: 1) the examination of the feasibility of ceramic membrane in treating restaurant oily wastewater; 2) the proposal of the filtration resistance model and development of non-stable prediction models for permeate flux and cumulative volume of permeate. On the feasibility research of ceramic membrane filtration, the effects of wastewater (feed solution) nature and operating conditions on the ceramic membrane filtration are identified. The contributions in this part of research are: 1. To understand membrane characterization by operating the filtration process under various separation conditions using pure water as feed solution; 2. To identify the effect of transmembrane pressure (TMP), crossflow velocity (CFV), oil concentration, temperature, salt concentration and pH on the permeate flux and permeate quality, and the influence of salt concentration and pH on the size and zeta potential of emulsion droplet as well. 3. To compare the effect of membrane cleaning under different chemical cleaner, and propose a protocol for membrane cleaning. 4. To design a plan for oily wastewater treatment with ceramic membrane technology. On the mechanism research of ceramic membrane separation, filtration resistances and four kinds of separation mechanism are reviewed. A new method to observe the variation of various resistances under different operating conditions is proposed. Models for predicting permeate flux and cumulative volume of permeate are developed. The contributions in this part of research are: 1. A new method to calculate the filtration resistances is proposed according to the different permeate fluxes determined in the various stages of the filtration process. The variations of filtration resistances under different operating conditions are presented. 2. Non-stable prediction models for permeate flux and cumulative volume of permeate are developed using one set of experimental data, and are verified using another set of experimental data. The results show good correlation between experimental data and predicted data. 3. The factor which has significant effect on the filtration process is identified using the sensitivity analysis method. This research has provided a theoretical basis and practical evidence for the application of ceramic membrane on the oily wastewater treatment. These experimental results will be of benefit to process design of oily wastewater treatment system, and contribution to the reduction of water pollution.