China is struggling to meet its drinking water supply demands in the face of population growth, urbanisation and rapid industrial development that have resulted in a shortage of water for approximately 400 cities.  Water resources per capita are 25% of world average, and even less in the northern and coastal areas (10 to 3.3%, respectively).  A severe drought in 2000 caused many reservoirs and rivers to dry up, while provinces and cities such as Jiangsu, Guangdong and Shanghai have faced serious deterioration in raw water quality.  Consequently, the Chinese government has legislated that major industry, including power stations, must re-use secondary effluent for process water.

Chapter 5 of the 2002 Water Law in China required all industries to extensively reuse water and increase water recovery, especially during new construction or plant upgrades. For the iron and steel industry, the regulations specify water intake lower than 16 cubic meters per ton (m3/ton) of product, and water reuse ratio higher than 90%.   In January 2005, the Chinese government imposed a new water consumption ratio on seven industries. These industries can now be charged a fee for any consumption of water over the allocated amount. If the situation is not rectified within a specified timeframe, the offending enterprises will lose access to the water supplies.

In order for reuse projects to be economically and ecologically successful, they must employ technologies that offer long-term reliable operation, have low operating costs, reduce or eliminate the use of chemicals and be as compact as possible.  Many reuse plants are either constructed on the same premises as existing wastewater treatment facilities or in areas where large space is simply not available, and therefore, have little room for implementation.

Treatment Technologies

There are a number of proven technologies for water reuse applications, including clarification, granular media filtration, carbon adsorption, low-pressure membrane filtration, reverse osmosis (RO), membrane bioreactors (MBR) and disinfection.  The choice of technology depends on the ultimate use of the reclaimed water.  Water for industrial use will have higher quality requirements than irrigation, for example.

Multi-barrier filtration systems, consisting of settling, clarification and granular media filtration, were typically used in reclaim applications.  Treated wastewater, however, is generally high in total dissolved solids and not suitable for direct or indirect reuse applications such as industrial consumption.  For this reason, RO is being used increasingly in advanced reuse facilities worldwide. 

In the 1980’s, low-pressure membrane filtration became economically viable as communities adopted this technology for filtering surface and groundwater for potable use. The exceptional performance of membranes in removing particulates resulted in their use as pretreatment to RO in potable or indirect potable reuse applications. 

Membrane Plants in China

Membranes offer several advantages over conventional treatment systems, such as a compact design, lower installation cost, reduced cleaning and replacement of the RO membranes, and lower overall life-cycle cost. Life-cycle cost savings result from reduced process steps and chemicals required to achieve high quality water.  The membranes’ compact design translates into a smaller system footprint, which becomes increasingly important to plants with limited space for expansion.  The superior performance produces RO feed water with a lower solids loading, which results in a lower fouling rate of the RO elements and longer RO element operating life.  All these features make membranes attractive to, and widely accepted by, industrial plants in China that need to achieve high quality process water, while reducing costs and space requirements.

In the last seven years, Siemens has installed more than a dozen membrane plants in China for reuse applications.  These are summarized in Table 1.  Membrane pilot plants have been engineered and installed in the Tianjin region for treating secondary effluent for industrial process water.  The first of six such plants in the region was commissioned in 2002 at the Ji Zhuang Zi treatment plant. Ten membrane filtration systems, plus ozonation systems, treat up to 20 MLD of secondary effluent.  The reclaimed water is being used in the Mei-jiang residential district for flushing toilets and watering gardens, and for an agricultural irrigation project in Jing-hai County, and for cooling water in the Chen-tang-zhuang heat and power plant.  Other uses are for an urban ornamental body of water, irrigation at the Cheng-lin nursery and for car washing stations.

The second pilot plant in the region for reclaimed water production treats secondary effluent for the Tianjin Economic Development Area (TEDA).  The reverse osmosis (RO) and membrane plant treats 20 MLD for non-potable municipal use and 10 MLD for industrial use.  This plant is designed for a future capacity of 40 MLD. The TEDA reclamation plant is the first full-scale system in China that uses a dual-membrane process for a reuse application.

In 2007, the third reclaimed water system in the Tianjin region was commissioned at the Xianyanglu treatment plant.  The 50-MLD submerged membrane system provides 40 MLD of non-potable water for municipal use and 10-MLD to feed an RO system for industrial use.

The fourth installation in the region was commissioned in 2008 and treats secondary effluent for the Tianjin Yangliuqing Power Station.  A 50-MLD submerged membrane system provides 40-MLD of ultrafiltered water, with the remaining 10 MLD feeding an RO system for industrial use in the plant.

Also in the Tianjin region, the Dagang Oil Field is using a submerged membrane system to treat a 50-50 combination of oil industrial waste and local municipal secondary effluent.  Commissioned in 2009, the system was designed and installed following a successful nine-month pilot system operation in 2006.

In Shanxi Province, the capital city of Taiyuan is experiencing a serious shortage of fresh water, prompting city officials to choose a membrane system to treat secondary effluent for its power station.  A submerged membrane system, commissioned in 2006, treats 15 MLD of a mixture of industrial and municipal effluent.  Three membrane systems pre-treat an RO system; the design flux ranges from 36.5 to approximately 50 liters per square meter per hour (LMH) for handling high suspended solids spikes in the feed water.

The Fuxin Power Station in Liaoning Province is using a submerged membrane system to provide reclaimed water, thus reducing the demand on the fresh water supply.  Installed in 2006, the system treats approximately 35 MLD of a mixture of industrial waste (dirty mine well water, wash water and polluted river water) and municipal secondary effluent within the plant. The treated water is then used to pre-treat an RO system that provides boiler feed water.

In Inner Mongolia, the Guodian Dongshen Power Station is using reclaimed water for its process water.  The submerged membrane/RO system was commissioned in 2008.

The steel industry in China is also benefiting from reclaimed water use. The Taiyuan Steel plant in Shanxi Province and the Handan Steel plant in Hebei Province are both using a submerged membrane/RO system for treating a 50-50 combination of industrial and local sewage secondary effluent.  Commissioned in October 2009, the Taiyuan plant provides approximately 50 MLD of treated water for reuse in the plant.  At the Handan steel plant, commissioned in November 2009, the system provides approximately 48 MLD of treated water for reuse.



These reuse projects are an example of a growing trend in China of using membrane treatment to meet the country’s water quantity and quality needs for a number of industries, from power stations to steel plants, while preserving scant drinking water supplies.

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