10 Water/Wastewater
Water Pollution in Asia – A Brief Review of Monitoring Technologies
The pressure on water resources is increasing rapidly. Nowhere is this more felt than in Asia, home to 60% of the world’s population. Safeguarding and managing these precious water resources is receiving increasing priority. As part of this drive, increasing numbers of water quality monitoring instruments are being deployed. This paper presents an overview of the various types of technologies used for the monitoring of surface waters in Asia.
A great number of technologies and systems are available for water quality monitoring.
Asia faces a serious and growing water quality challenge. Rapid population growth, urbanisation and industrialisation in the region threaten to limit the freshwater supply. Strong seasonal variations in precipitation due to monsoons and inadequate water and wastewater treatment facilities compound these issues even further. For example, one third of China’s main river systems have water of quality with very limited or no functional use, and in the water-scarce northern provinces 40 to 60% are permanently classified as non-functional.1
In countries
such as Japan and South Korea, which have comprehensive sanitary facilities and wastewater treatment, pollution is less severe. Nevertheless, their water resources are under pressure from elevated nutrient levels and trace contaminants, such as pesticides and pharmaceuticals. The only river systems that remain largely untouched are the upper reaches of rivers in Indochina, such as the Mekong. However, increasing development in countries such as Cambodia and Laos is now starting to compromise water quality even in those few remaining pristine rivers.
Effective management of the water sources requires information and understanding. Water quality monitoring networks are in place across the entire region; for example, both India and China maintain networks with thousands of monitoring sites. Despite the impressive numbers, however, spatial coverage remains sparse due to the size of the continent. Furthermore, monitoring consists primarily of infrequent manual analysis of a few physical-chemical parameters suited neither to map out the dynamics of water quality variability nor to properly assess chemical and biological quality. This is becoming increasingly apparent, and both China and India are investing in setting up networks of stations for continuous water quality monitoring. For example, in its 11th Five Year Plan, the Chinese government intends to establish an advanced environmental monitoring system, equipping all key sources of pollution with automatic monitoring instruments. More recently, the World Bank has awarded the River Ganges Improvement Contract to set up a network of online monitoring stations along India’s River Ganges, and the Taiwanese EPA initiated the installation of real-time monitoring systems at 114 large-scale enterprises around the country to monitor violations of its Water Pollution Control Act.
Traditional Monitoring Parameters
The measurement of basic physical-chemical parameters is by far the most widespread application of on-site water quality instrumentation. Parameters such as pH, EC, DO, ORP and temperature can be measured using handheld meters or with online sensors. A trend can be observed towards the use of multiparameter probes, which combine small sensors into a single submersible instrument. Another development is the arrival of the optical DO sensor. The advantage of all these systems is their long-term stability and low sensitivity to fouling, thus reducing maintenance, bringing down lifecycle costs while at the same time increasing up-time and reliability.
High levels of precipitation during monsoons as well as erosion from the Himalayas result in high levels of suspended solids in many of Asia’s rivers. Variable levels of suspended particles can be detected by turbidity and TSS sensors, which typically use an optical transmitter with a red or NIR light source, and measure the light absorption of the particles in the sample. Alternatively, sensors which measure light scattering (e.g. at a 90o solids and turbidity.
angle) can be used for lower concentrations of
All these instruments are available from any of the major water monitoring instrument manufacturers. Also, instruments for these traditional monitoring parameters are widely available from local manufacturers, who have a substantial share of this market. In contrast, the market for more advanced systems (see below) remains dominated by US and European manufacturers.2
Nutrients Author Details:
Joep van den Broeke Benten Water Solutions
Emails:
jvandenbroeke@benten-water.com Tel: +31 (0) 85 877 0386
Figure 1: Floating monitoring station, Yangtze River, China. AET Annual Buyers’ Guide 2013
www.envirotech-online.com
Elevated levels of nutrients, mainly as a result of fertiliser use, pose a serious problem for water quality. For the monitoring of the nitrogen levels in river water, ion selective electrodes (ISEs) are currently the preferred option. Both ammonium and nitrate, the primary contributors to the nitrogen load in river water, can be measured using ISEs. These have matured into a stable and robust sensor technology which can be used under rough field conditions, with an average maintenance period of between 3 – 6 months. The main issue of concern, especially for ammonium, is cross-sensitivity of the electrodes to interfering substances. Advanced sensors use additional electrodes to measure and compensate for this interference. Alternatively, UV spectrometers can be used to monitor nitrate. Both the advanced generation of ISEs as well as the optical instruments are available from manufacturers such as Hach, s::can and WTW.
Cabinet Analysers
Currently, the other important nutrient, orthophosphate, can only be measured using online analysers. An analyser is an automated and/or miniaturised system to perform a classical laboratory analysis, such as a titration. The reagents dosed to the sample react with the substance of
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