Management, disposal and recycling of waste industrial organic solvents in Hong Kong

Abstract

An attempt has been made to establish a mass balance of industrial organic solvents in Hong Kong. It is estimated that only a small portion, less than 4%, of all the organic solvents consumed in Hong Kong are collected as waste solvents and properly treated, while the remainder are used either in the formulation of solvent containing products, or are lost to the environment through vapour emissions, leaks and spills, or dumped illegally. It was found that solvent recycling has been a common practice in some industries but the existing level of solvent recycling in Hong Kong is difficult to estimate. About 87.4% of all the waste organic solvents disposed of at the licensed facilities are potentially recyclable although whether they can be recycled in practice depends on many factors. Examples of existing waste organic solvent management and recycling practices from selected industries in Hong Kong are presented. The economic feasibility of current and future potential recycling systems is evaluated for a few selected cases. An integrated waste organic solvent management strategy is proposed to minimize adverse impacts of organic solvents to the environment and human health.

Introduction

Organic solvents have been widely used in various industries. Their main applications include formulation of products, thinning of products prior to use, and cleaning of materials by removal of contaminants (Siva, 1990; Callahan and Green, 1995). During these applications solvent emission and waste solvent generation occur. Most organic solvents and their emissions/wastes are known to have adverse effects on both human health and the environment (Burrell, 1990). Solvents may affect the body through inhalation or skin contact and lead to either acute or chronic poisoning. The effects of acute poisoning include narcosis, irritation of throat, eyes or skin, dermatitis, and even death and the effects of chronic poisoning include damage to blood, lung, kidney, the gastrointestinal system and/or nervous system, etc. (Alliance, 1987; LD, 1996). There are two groups of adverse impacts of organic solvents to the environment. One includes those due to the emissions of the solvents to the atmosphere (VOC emissions) and the other due to the damage of solvents in liquid form when they pollute the surface water, soil, underground water or marine water (Heslinga, 1992). Stratospheric ozone depletion and global warming are two major impacts to the environment due to VOC emissions (Epson, 1993; USEPA, 1995, USEPA, 1996; AFEAS, 1996). However, while ozone in the stratosphere is beneficial to the earth and its inhabitants, the tropospheric ozone formed by photochemical reaction with VOCs as precursor is a pollutant which can penetrate deeply into the respiratory tract and cause various adverse health effects including eye irritation, cough, reduced physical performance at low concentration and edema, bronchitis and chromosome abnormalities of white blood cells at high concentration (Heslinga, 1992; Callahan and Green, 1995).

In addition to the adverse effects on human health and the environment, many solvents are inflammable in nature (Durrans, 1971; Archer, 1996; LD, 1996; FSD, 1997). Proper management and disposal of waste organic solvents are therefore very important. Generally, the waste management options include source reduction, recycling, treatment and disposal in descending order of desirability (Wyman and Register, 1988). All these options have been successfully applied to waste solvent management in many cases around the world. Examples include the switching of solvent cleaning to no-clean technology in the electronics industry (Sprow, 1993), the use of abrasive to replace solvent in mould cleaning (ASM, 1996), aqueous detergent to substitute solvents in vapour degreasing (Snyder, 1990), less hazardous hydrocarbon and oxygenated solvents to replace ozone-depleting halogenated solvents in many applications (Schreiner, 1990), better operating practices to reduce drag-out solvents (Callahan and Green, 1995), improvement of processing equipment to minimize VOC emissions (Heslinga, 1992), various solvent recovery and recycling technologies to extend the service life of solvents (Breton et al., 1988), the use of waste-derived fuel extracted from waste solvents in many high temperature industrial processes (Breton et al., 1988; Green, 1997), and so on.

In Hong Kong, waste organic solvents are categorized as chemical wastes which must be collected by licensed collectors and disposed of at licensed facilities (EPD, 1992). Since the commissioning of the Chemical Waste Teatment Centre (CWTC) in April 1993 until the end of 1997, about 18,000 tonnes of waste organic solvents have been treated there (EPD, 1998 and earlier Editions). It can safely be assumed that some waste organic solvents have been treated at other licensed facilities and some have been disposed of improperly.

Following a global trend of using less hazardous solvents, less harmful substitutes with similar effectiveness have been developed to replace some of these harmful solvents (Burrell, 1990). However, for those solvents for which no suitable substitutes have been developed, the users are facing high solvent purchase costs and increasing disposal costs. The current charging rate at the CWTC of approximately 2800 HK$/tonne of organic solvent recovers only 31% of the Variable Operating Cost. Considering that the recovery rate of Variable Operating Cost will be gradually increased to 100% by the year 2003/04 at the latest, that the prices of environmentally hazardous solvents are increasing and that the prices of environmentally friendly solvents are still high, solvent recycling appears increasingly attractive to the solvent users or the waste solvent producers.

The purpose of this study was (i) to estimate the consumption, emission, recovery and disposal of organic solvents in Hong Kong for the establishment of a mass balance, (ii) to evaluate actual practices and future potential of waste organic solvent recycling in Hong Kong, and (iii) to propose and evaluate an efficient and environmentally sound management strategy to handle waste organic solvents in Hong Kong.