TITLE : ZERO LIQUID DISCHARGE TECHNOLOGIES & ECONOMICS

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1 TITLE : ZERO LIQUID DISCHARGE TECHNOLOGIES & ECONOMICS Author : Soham Mehta Managing Director Advent Envirocare Technology Pvt. Ltd. A-1, 8th Floor, Safal Profitaire, Corporate Road, Prahaladnagar, Ahmedabad Phone: advent@adventenvirocare.com Website : Abstract : Zero Liquid Discharge is more of a compulsion than choice for industries, often requiring hasty decisions and execution. Understanding the concept of segregation of streams and addressing the segregated stream according to its characteristics is the most efficient approach, both in terms of performance and cost. Evaluation of streams and budgeting the capital and operating costs based on stream management is an exercise that takes time but gives proper direction whenever it calls for implementation of ZLD system.

2 Zero Liquid Discharge is a compulsion being faced by many industries, either due to products they manufacture, or mostly due to lack of any approved receiving body for disposal of treated effluent. This expensive compulsion is generally manifested as a crisis, and industry is concerned to take a hasty decision and execute the project with even more haste. This paper aims at providing quick reference on technologies or processes that can be adopted depending upon the candidate stream of effluent, and the indicative figures for capital and operating costs. ZLD Basic Stream Segregation The operating cost of a ZLD System is usually governed by thermal treatments such as Evaporation and Incineration. To optimize on this, streams with higher concentrations of organics and salts should be identified, segregated at source and treated either separately or mixed with other concentrated streams for eventual disposal using thermal treatments. Typical treatment processes for segregated aqueous streams are presented below : Table 1 : Treatment of High Strength Effluent Streams Stream Characteristics High salt (TDS > 5% or 50,000 mg/l) with any concentration of non-volatile organics (expressed as COD) High salt (TDS > 5% or 50,000 mg/l) with volatile organics exerting COD > 25,000 mg/l High salt (TDS > 5% or 50,000 mg/l) with volatile organics exerting COD < 25,000 mg/l Treatment Process Multiple-effect Evaporator with dewatering of residual salt; this stream can be mixed with RO Reject Single-effect Evaporator with dewatering of residual salt and thermal oxidation of vapours; about 40% of the heat can be recovered by pre-heating the vapours using exhaust gases Multiple-effect Evaporator with dewatering of residue and treatment of condensate in biotreatment system

3 High COD (>50,000 mg/l) exerted by volatile organics or mixed organics High COD (>25,000 mg/l) exerted by nonvolatile or non-degradable organics. High COD (>20% organics) exerted by any type of organics High COD (> 10% non-volatile organics) alongwith high TDS ( > 5% inorganic salts) High COD (> 10% non-volatile organics) alongwith high TDS ( > 5% inorganic salts) Single-effect Evaporator with dewatering & incineration of residual salt and thermal oxidation of vapours; about 40% of the heat can be recovered by pre-heating the vapours using exhaust gases. Multiple-effect Evaporator with incineration of residue Incineration, followed by heat recovery Multiple-effect evaporator with incineration of residue Single-effect evaporator with thermal oxidation of vapours and dewatering of residual salts; salt to be bagged and disposed to landfill Apart from these, there are possibilities of recovery of organics using processes such as solvent recovery. There may be other streams which can be segregated or may need to be segregated inspite of having little lower TDS or COD. These streams shall have to be addressed with respect to overall Effluent Management System. Low Strength Stream Recycling Segregation is equally useful while dealing with low strength effluent after removal of high TDS and high COD streams. Usually, utility streams such as blow-downs, ion-exchange regenerants, utility RO rejects and vacuum pump bleeds can be treated separately in a rather simplistic system while organically-contaminated streams can be handled with more elaborate treatment process. Typical approaches are as per Table 2.

4 Table 2 : Lean Stream Treatment Stream characteristics Low TDS (<10,000 mg/l) without any organic contamination Low TDS (<10,000 mg/l) with low to medium COD (<10,000 mg/l) without solvents Low TDS (<10,000 mg/l) with low to medium COD (<10,000 mg/l) with presence of solvents Treatment process Pretreatment for removal of TSS, metals and hardness, followed by pressurized ultrafiltration and Multi-stage Reverse Osmosis; reject from RO to be handled in MEE Pretreatment for removal of TSS, metals, hardness, etc., followed by Membrane Bioreactor and Multistage RO; reject from RO to be handled in MEE Pretreatment for removal of TSS, metals, hardness, etc., followed by High Rate Bioreactor, Membrane Bioreactor and Multi-stage RO; reject from RO to be handled in MEE ZLD Economics Typical budgetary estimates for all-inclusive capital and operating costs for various equipment used in ZLD systems are provided in Table 3 (valid for m 3 /d systems) Table 3 : Capex & Opex For ZLD Components System Budgetary Capex Budgetary Opex Pretreatment system for Low-strength streams Pressurized UF for low strength inorganic stream Rs. 20 to Rs. 30 per litre of Rs. 5 to 10 per litre of Usually less than Rs. 10 per 1000 litres of effluent Rs. 5 to 10 per 1000 litres of effluent

5 Membrane Bioreactor for low strength stream Multi-stage RO for lowstrength stream MEE for RO Reject of lowstrength stream MEE for High-strength effluent Single-effect Evaporator for High-strength stream, with Thermal oxidizer for vapour Incineration for MEE residue Incineration for high COD aqueous effluent Rs. 40 to 60 per litre of Rs. 10 to 20 per litre of Rs. 100 to 150 per litre of reject fed to MEE per day (using titanium tubes will cost 30-50% more) Rs. 100 to 150 per litre of effluent (using titanium tubes will cost 30-50% more) Rs. 250 to 400 per litre of effluent (using titanium tubes will cost 15-25% more) Rs. 800 to 1200 per kg of feed per day Rs. 800 to 1000 per litre of feed per day Rs. 5 to 10 per 1000 litres of effluent depending upon the MBR configuration (including membrane replacement) Rs. 30 to 40 per 1000 litres of effluent depending upon the MBR configuration (including membrane replacement) Rs. 400 to 600 per 1000 litres of effluent fed to MEE, considering coal as fuel to boiler Rs. 400 to 600 per 1000 litres of effluent fed to MEE, considering coal as fuel to boiler Rs to 5000 per 1000 litres of effluent fed to MEE, considering coal as boiler fuel Rs. 10 to 20 per kg, without considering heat recovery Rs. 10 to 15 per litre, without considering heat recovery

6 Case History & Conclusion Zero liquid Discharge has been successfully and optimally demonstrated in many chemical process industries, including dyes, dye-intermediates, bulk-drugs, pesticides, fine chemicals, specialty chemicals, refineries, etc. and has been found to be economically viable proposition, though not favourable. In water intensive industries such as textiles, the cost of evaporation of large quantity of reject is the major deterrent, alongwith issues related to silicon & silicate fouling. Till an option is available, ZLD is not the solution for textile effluents in the current regime of water costs. However, partial recycling and segregation of high strength effluents such as dye-bath and first-wash can be employed to drastically reduce the pollution in receiving bodies. For industries located in the coastal areas, effluent recycling with disposal of saline RO reject into the sea can be a very attractive and sustainable option. Effluent Recycling and Zero Liquid Discharge Systems are here to stay, and sooner you start working on these, better are your chances to select the right configuration at a right cost.