TREATMENT OF SALINE WASTE-WATER FOR ZERO DISCHARGE AT THE DEBIENSKO COAL-MINES IN POLAND

The drainage water from mines in Poland has a daily contribution of, i n the order of magnitude, 6,500 tons of chlorides and 0.5 ton of sulph ates to the rivers Vistula (Wisla) and Oder (Odra). The largest amount s of these salts, about 78%, derive from 18 mines located mainly in th e Katowice mine district. The high salt content in the water from the Vistula prevents at present its use in agriculture and causes tremendo us economic losses due to corrosion attacks on pipes, machines, etc., within the industry. At present only about 4% of the river water can b e classified as drinking water. To combat this problem a desalination project in Katowice has now almost been completed, including advanced treatment of wastewater for zero discharge from the two adjacent coal mines, Debiensko and Budryk. It implies elimination of 310 tons/d of s alt discharge to the Odra River. The complete treatment processes are divided into three main sections: (1) pretreatment before reverse osmo sis (RO) of about 12,400 m(3)/d drainage water from the two mines with a salinity of around 16,000 mg/l TDS on the average; (2) RO plant inc luding posttreatment of the RO permeate; (3) a thermal plant for conce ntration of brine (about 4,600 m(3)/d) and separation of sodium chlori de (NaCl) by crystallization, centrifuging and drying. The RO pretreat ment includes algicide dosing in a storage tank, disinfection, floccul ation/sedimentation and dual media filtration as well as granular acti vated carbon filtration. After a two-stage microfilter system (50 mu a nd 5 mu, respectively), the pretreated water is desalinated at 6-7 MPa in a RO system with spiral wound RO membranes. The RO permeate is dec arbonated in a part-flow followed by addition of chemicals for disinfe ction and increase of the temporary hardness before distribution in th e drinking water net. The flow into the thermal plant consists of the RO reject (about 2,700 m(3)/d) with a salinity of around 80 g/l TDS an d the brine flow (about 1,870 m(3)/d) from the Budryk mine with about the same salinity. The first section of the thermal plant is composed of two brine concentrators, designed by Resources Conservation Company (RCC), USA. By using the seed crystal recycling technique it is possi ble to concentrate the feed to near the precipitation point for NaCl. The second section of the thermal plant includes one crystallizer for production of NaCl, two pusher centrifuges for salt removal from super saturated brine and one fluidized bed dryer. The crystallizer is a for ced circulation submerged-tube evaporator equipped with a mechanical v apor compressor. An additional section is also planned to be construct ed for treatment of the purge from the crystallizer in order to recove r other valuable chemical products and distillate. The process is full y automatic and controlled by programmable logic controllers. The plan t has finally been designed by Energotechnika, Poland, after preparati on of technical and economical planning of the project in coordination with Nordcap Ltd., RCC and VBB Viak-SWECO, Stockholm. In the summer 1 994 the thermal plant was started up, and the RO plant is expected to be in operation during the spring 1995. The paper covers the project d esign with illustrations of the main parts of the plant and summarizes the results of the initial operation.