Biological Oxygen Demand (BOD) is a satisfactory parameter to measure water quality. However, the process of measurement should be improved and speeded up. Two ways of doing this are using a bio-sensor based system or a spectrophotometer, that give results within minutes and are nearly as accurate as laboratory-based monitoring. That said, conventional laboratory testing must also be made more robust with clear protocols for sampling, transport and testing.
The Central Pollution Control Board should simplify the process of approving the use of BOD measuring equipment. Instead of a two-step process that is time-consuming, it will be recommended to have a single step, where the use of the process has to seek approval only from CPCB. Currently, equipment manufacturers have to get approval from both CPCB and the Bureau of Indian Standards, while there is no legal requirement for the latter organization to certify this equipment.
These are two of the outcomes of a meeting organized by the Centre for Science and Environment to discuss the existing protocols for monitoring water pollution (based on the BOD parameter) and equipment. The objectives were to find a way to advance the process of monitoring water pollution; assess if a better parameter than BOD was available or needed and; how BOD can be measured faster and more accurately than is done currently. The costs and benefits or using a new parameter would also have to be considered before suggesting a change.
One of the alternatives suggested was the total organic content (TOC) present in water since industry contests the results of the concentration of BOD in water found by the state pollution control boards. A drawback with TOC is that algal BOD causes errors in results, and this had become a major factor with increased use of detergents and fertilizers.
Bio-sensor
The Institute of Genomics and Integrative Biology, Delhi, have developed a bio-sensor based system to measure BOD. This has been calibrated against existing BOD5 tests performed in laboratories and the margin of error is +/- 10%. The reference test is with glucose glutamic acid (CGA) to measure dissolved oxygen (DO). There is a specially cultured collection of bacteria that can degrade the organic load of different types of waste water, both from industrial and domestic sources. This culture is immobilised on a membrane that lasts for up to two years in the field (the laboratory membrane has been in use for six years). This process eliminates the need to test for COD separately.
The first measurement takes about two hours and repeat readings can be done at 10-15 minute intervals. Sample solutions are buffered using phosphate as a source of oxygen and if the result from the sample if out of range, then a smaller sample with great dilution is used. The system has improved the stability of the microbial membrane from a few months to more than two years. In the system, an immobilized microbial membrane attached to oxygen probe is immersed into oxygen saturated buffer solution. Oxygen concentration as current output is recorded. On addition of a waste-water sample, the respiration activity of microbes increases due to assimilation of organic matter by immobilized microbes and the concentration of oxygen near the membrane decreases. Difference in oxygen concentration is directly proportional to the concentration of the organic matter in the sample. The deviation from BOD5 measurement is a maximum of about 7%.
Biomonitoring
This can be used as a proxy for assessing water quality. It was developed to expand monitoring in other areas where there are no laboratories. The concept was to have simple protocols for water quality monitoring that include fish, algae, colour, turbidity, etc., that vary with quality. These could be followed by laboratory testing where necessary. Biomonitoring can be used as replacement for BOD where toxicity in water is so high as to kill off all micro-organisms making it impossible to test BOD. For example, the Central Pollution Control Board used it to assess the water quality of Krishnareddypet in Hyderabad in 1995 that had been severely contaminated by pharmaceutical effluents. The best time for biomonitoring is better December and May, or till the monsoons start, as this gives time for micro-organisms to re-establish their colonies. It is the cheapest way to monitor for pollution because local communities can be taught the indicators in just two weeks. Biomonitoring relies on benthic organisms that has limited mobility and are therefore good indicators of local water quality.
Spectrophotometer
Spectrophotometer-based BOD monitoring systems are also available now that give instant values. The device scans a range from 200 - 750 nanometres and has been calibrated using potassium dichromate. It can identify the major BOD components, temperature, pH, nitrates, chlorophyll-a, algae, dissolved oxygen, conductivity, TDS, turbidity and color at different depths and for different water bodies. Instead of an offline system where samples are taken to a laboratory, this system uses a solid-state probe that is inserted into the waste water or river stream. This is however, not a replacement for laboratory testing, but a quicker means of assessing water quality.
The Central Pollution Control Board is expanding its pollution monitoring network. The goal is to have one monitoring station every 10 km on the main stem of a river, and every 20 km in each tributary; the total number will be 10,000 stations. Some will be automatic, while others will continue to be manual. The testing scope will also be expanded, with nine core parameters being measured each month, 20 others every quarter and 25 parameters every year. This will include heavy metals and pesticides as well. The Central Government will provide 70% of the funds, while states will provide the rest. In the north-eastern states, the Centre will provide 100% of the funds.
The approximate cost using current laboratory testing methods is Rs 5,000 per sample for 9 parameters. CPCB is testing 10 spectrophotometer stations over two years, two on the Yamuna (in Delhi) and eight on the Ganga at major cities. The capital cost is about Rs 3 crore and an additional 2.5 crore will be used to set up a data-centre, that can be used for the larger monitoring network. The private company contracted for the monitoring will sell the monitoring data to CPCB and be responsible for the maintenance of the network.
The first water quality standards for rivers were developed in 1978. The approach was to assign a specific beneficial use to various stretches of water-bodies and develop criteria to protect that use. For all stretches of water the beneficial use requiring the highest quality was identified as the “Designated Best Use (DBU)” and the criteria applicable to that use were applied. There were several problems with its implementation: the health of eco-system was not covered; the scheme only looked at organized use while a large population in India depends on un-organized use and uses water for multiple purposes and; it was difficult to identify DBUs with the more than 5000 rivers, 20000 lakes and ponds and a large number of aquifers in the country.
Therefore, this was revised in 2001-02 and eight regular parameters were to be monitored as frequently as possible, including pH, dissolved oxygen (DO), BOD, conductivity, nitrates, TSS, fæcal coliform and bioassay. Another 16 special parameters were to be monitored on a need basis including nutrients, heavy metals, pesticides and organic and inorganic toxicants.
BOD is an overarching parameter that provides an insight into the overall biodegradable organic content and its impact on aquatic life and water quality. Therefore, the standard for dissolved oxygen is used for assessing and reporting compliance of rivers, and that the standard for BOD is used for deciding action to meet the standard for dissolved oxygen in the river. One of the problems cited with B.O.D. is the accuracy and precision of its measurement. While this is true it could be overcome by a detailed analysis of its relationship with other parameters which are relatively more accurate and precise such as Chemical Oxygen Demand (C.O.D.) or Total Organic Carbon (T.O.C.).
Discussions
The discussions on retaining BOD as the yardstick for monitoring water quality highlighted its usefulness as a summary parameter of water quality since this measures the rate of use of oxygen. BOD is a replacement for natural processes as it measures the amount of carbon that demands oxygen for decomposition in water. It is a combination of various biological solids and effluents in water. On the other hand, total organic carbon is not a regulatory parameter and harder to measure. BOD is important at the level of a riverine ecosystem. However, the process of measuring BOD can be improved using the new techniques described.
BOD and COD are the measures of the stress of an aquatic ecosystem. However, it can be inadequate to measure the health of such a system, while dissolved oxygen may be a better parameter. Thus, BOD is more appropriate for measuring the performance of effluent treatment plants. This can be summarised as dissolved oxygen is an indicator of the health of the system, while BOD indicates what action is needed to improve the health. A water quality index can be developed that is a composite of different parameters, and the cost of measurement can come down with improvements in technology. The Bureau of Indian Standards has protocols for checking BOD that need to be revised. However, there is no procedure to standardise the methods and analysis.
At the moment, equipment to measure BOD has to pass through two stages of certification, first with the CPCB and subsequently with BIS. This is a convention without any legal requirement and needs to be rationalised to speed up the improvement of monitoring BOD. The onus for getting regulatory clearances should be on the end-user, who must convince the authorities about the efficacy of the equipment.
A series of meetings on water quality is planned over the next few months to take forward the specifics.
The following people attended the meeting:
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