Water & Wastewater Asia May/Jun 2018

WATER & WASTEWATER ASIA May / June 2018 OPINION / 39 By Professor V.Aksenov, PhD 1 ; A.Denisov 2 ; I.Nichkova, PhD 1 ; Y.Denisov, PhD 1 I n the last 10 to 15 years, a trend to install closed water supply systems (CWSS) or Zero Discharge Systems (ZDS) at industrial facilities became evident in countries with mature wa t e r managemen t cu l t u re . There are a few reasons for the growing popularity of ZDS projects: increase environmental impact from contaminated industrial, municipal and agricultural wastewater, advancements and technological developments in wastewater treatment process, and improved economic viability of ZDS projects through reliable and predictable performance. At the same time, a broader variety of process equipment (such as multiple- effect evaporator systems and RO technology) became available, which made CWSS installations more attractive from the economic benefit perspective. Criteria for economic efficiency at ZDS plants include low consumption ratio, low CAPEX, high labour efficiency, and scalability for operational growth. One of early ZDS projects, which successfully implemented at a metallurgical plant, goes back to 1973 in Ekaterinburg city, Russia – that installation is still operating today [See Fig. 1: 1-5]. The facility was designed to produce cold- rolled steel with compulsive etching process, creating a complex chemical composition, including sulphates, sulphuric acid, chlorides, hydrochloric acid, and iron. One of the key project requirements was to neutralise eco-impact from the plant on the environment and municipal water. For example, steelmaking plants commonly generate eight types of wastewater: 1. Insulation coating sets and decarburising annealing sets, containing fine magnesium oxide; 2. Rinse waters from mill casings, containing oils and suspensions; 3. Acidic iron-containing rinse wa t e r s f rom t he e t ch i ng workshop; 4. Waste etching solutions; 5. Waste oil emulsions; 6. Waste degreasing solutions; 7. Rinse waters from degreasing units; 8. Rinse waters from oil emulsion systems. Based on the type of contamination, wastewater can be combined into the following four groups: • Waste etching solutions; • E t c h i n g wo r k s h op r i n s e solutions; • Wastewater, mainly containing suspended substances; • Oil-containing waste waters. The corresponding treatment plants for each type of waste were designed and located in different buildings (see Fig. 1). ZDS flow-chart at this facility: 1 - Incinerator for industrial lubricants; 2 – Evaporator; 3 - WW treatment plant; 4 -Rolling plant; 5 - Chemical treatment; 6 - Boiler plants; 7 - Treated water (clean water); 8 - Pump station, located on the city pond. Among all types of contaminants, found at the metallurgical plants, acidic iron-containing rinse water from the etching workshop is the Fig. 1: Diagram of zero discharge system for water management at a metallurgical plant.