Wastewater Treatment Glossary: Mine Water
To strengthen coal-mine wastewater treatment and protect the aquatic environment, newly built mines attach great importance to environmental-protection construction and have invested substantial funds. Design units have also carried out multi-process, multi-scheme comparisons and exploration for domestic sewage treatment.
For a given mine, sewage pipe networks and sewage-treatment plants should be built in phases and batches according to the mine's overall plan and drainage plan, implemented phase by phase in line with water-environment protection goals, and gradually brought up to standard.
(1) At present, some coal mines build a separate sewage-treatment plant for the industrial site and the residential area, requiring two land appropriations, duplicated construction, increased investment, high operating energy consumption, high management costs, scattered technical strength, and high per-ton water-treatment cost. Generally, the mine industrial site and the residential area are not far apart, so it is more reasonable to jointly build one sewage-treatment plant of a certain scale. Considering that drainage from the residential area to the industrial site would require very deep pipe burying, an intermediate sewage-lifting pumping station can be set up, or the plant can be built on land in the middle area between the industrial site and the residential area. The joint-build approach not only saves investment but also greatly reduces operating costs.
(2) Many newly built mine designs have a small labor quota according to codes and overall efficiency, but after actual completion the mine recruits a large number of contract workers, and with the mine's development a large number of outside personnel pour in, increasing the mine's water consumption and consequently the sewage volume. Therefore, when designing a new coal-mine sewage-treatment plant, a reserve coefficient should be considered in determining the construction scale.
(3) Because coal-mine wastewater quality and quantity vary greatly, reasonably determining the designed sewage volume and quality is directly related to project investment, operating costs, and cost-effectiveness. Production sewage and domestic sewage should be considered together, without excessive reserve margin, to avoid increasing investment and leaving equipment idle or running at low efficiency.
Generally, the effluent requirements differ considerably among mines and should be determined according to the requirements of China's environmental-protection authorities to ensure effluent quality. Because nitrogen and phosphorus in domestic sewage cause eutrophication of water bodies, sewage treatment is required to achieve nitrogen and phosphorus removal.
Coal-mine wastewater is similar in nature to general municipal sewage, but differs from it (municipal sewage often includes some industrial wastewater). Its characteristics can be summarized as: large variation in quality and quantity, low pollutant concentration, good biodegradability of the sewage, and low treatment difficulty.
Mine sewage-treatment plants designed in the 1980s mostly adopted the activated-sludge process; because the organic content of the sewage was too low, the microorganisms could not obtain the minimum nutrients during operation, so activated sludge could not form and the plant could not run. The oxidation-ditch process had the same problem: the return activated sludge could not be recirculated, turning the original oxidation-ditch system into an add-on aerated banded horizontal-flow settling tank, failing to meet the required treatment target.
In the 1990s many mines adopted the two-stage biological contact oxidation process to treat coal-mine domestic sewage, with very good results. This process adapts to low-concentration, highly variable mine sewage, while saving investment and being simpler to operate and maintain than the activated-sludge process, but its nitrogen and phosphorus removal is poor.
Since the 1990s, research, development, and application of new biological wastewater-treatment processes and technologies have achieved great success, and many new processes have emerged. The common features of these new processes are: high efficiency, stability, energy savings, and multifunctionality including nitrogen and phosphorus removal.
As is well known, water scarcity has become a global problem. China also faces the reality of water shortage. Sewage recycling and reuse is one of the effective ways to improve the comprehensive utilization rate of water resources, ease the contradiction of water shortage, reduce water-body pollution, and achieve sustainable use of limited water resources. After coal-mine wastewater is treated and disinfected, it can be used for greening, washing, and industrial water. Using the BAF process to treat coal-mine wastewater gives stable effluent quality, superior to general traditional biological treatment processes; after disinfection the effluent can be reused as reclaimed water.
, direct investment per m3 of sewage is about 1,000 yuan, while using the BAF process can control it at about 500 yuan, and it can save nearly 4/5 of the footprint. Coal-mine wastewater varies greatly in quality and quantity, has low pollutant concentration, and has good biodegradability, so the BAF process is quite suitable. [1]
The biological aerated filter (BAF) process features small volume, land savings, high efficiency, good effluent quality, simple flow, and convenient operation and management. In actual operation it can achieve central centralized control and on-site manual/automatic control. After multiple engineering applications, it has become increasingly mature; its effluent, after disinfection, can meet the reclaimed-water reuse standard. It is understood that at present in China each treatment of
