Last week I was in the chamber of Member Secretary of one of the progressive State Pollution Control Boards in India. A discussion was ongoing to set effluent standard for COD for a pulp and paper mill upstream the water intake of a major city. The discussions centred around modelling of COD from the point of effluent discharge to the point of water intake and arrive at the COD limit.
I found the discussion not focusing on the real issue. The impact of COD on the generation of disinfection by products (DBPs) leading to potential THMs and associated health risks in the water supply was completely missed out. Hence this post …..
Most rivers in India are today polluted. Untreated domestic wastes, industrial effluents and agriculture return waters have been the principal sources of pollution. Dumping of solid wastes has also been an important contributor.
To top, indiscriminate withdrawal of river waters is carried out for the interest of irrigation, power generation and industrial consumption. This has led to reduced river flows offering less dilution and low flushing velocities. Importance of maintaining “environmental flows” is generally discussed only in the conferences and serious attempts towards setting policies to this effect are not seen. Will we ever see?
River water quality is understood through basic parameters like Dissolved Oxygen (DO), Biochemical Oxygen Demand (BOD), Most Probable Number (MPN) of Coliforms and pH. Classes of water quality are defined based on the levels of these four parameters.
Water quality is considered to be Class A when DO > 6 mg/l, BOD < 2 mg/l, MPN < 50/100 ml and pH in the range of 6.5 to 8.5. Water of class A could be used or consumed with minimal or no treatment. You would hardly expect to see Water quality Class A in the river stretches of India. Perhaps, that’s a dream not to come true.
So, we need to treat water before consumption for drinking. Water treatment plants are designed, installed and operated at the locations of river intakes and only then water is transported to serve the population in cities. We want water we drink to be “safe”.
Water treatment plants are designed to meet the drinking water quality standards. These standards are guided by the Indian Standard IS 10500. Amongst the several parameters listed, the principal parameters where standards are specified include Turbidity, MPN of Coliforms, pH, Total Dissolved Solids (TDS), Iron, and Nitrates etc.
Performance of the water treatment plant depends on the quality of water it receives. Worse is the quality of raw water, more are the efforts expected on treatment of water. Dose of chemicals e.g. for flocculation and disinfection increases as pollution increases. Cleaning of the filters is more frequent generating more backwash water and longer retention times may have to be maintained in disinfection units. All this adds to the cost of operations.
More importantly, since most water treatment plants are designed as conventional, several specific pollutants such as metals, AOX etc do not get intercepted or treated posing risks to the consumer. This risk is rarely understood and not adequately addressed. In some of the States in India, water intake works have been shifted “upstream” due to the problem of increasing pollution downstream. But is this way to “solve” the “problem”?
Pollution in rivers has thus indeed influenced the water treatment works in India both on costs and efficiency. The risk of supplying safe drinking water has steeply increased.
The true cost of not treating pollution upstream can be significant to the downstream population or the water users. Somewhere someone saves moneys and somebody else pays elsewhere! This has always been a differential, a skew and a case of inequity requiring an inquiry in the economics of environmental management.
We need to take a systems perspective. Unfortunately, agencies that manage pollution do not interact with water works agencies. They need to talk and work together.
Let us take BOD as a parameter of concern for expressing the level of pollution in river waters. This parameter is understood better when we connect it with Chemical Oxygen Demand (COD). Both BOD and COD are not generally measured at the intake of water treatment works. An associated parameter is Total Organic Carbon (TOC) that provides further insight. Few water treatment plants that operate sophisticated disinfection systems and tertiary treatment processes measure TOC.
BOD, COD and TOC show relationships and one can set up “regression models” to map one from another when data is collected over time.
Higher is the value of TOC, higher is the dose of chlorine required in the process of disinfection to ensure destruction of Coliforms and to maintain desired levels of residual chlorine. The cost of operating disinfection unit increases as the TOC in the raw water goes up – which is the result of pollution released “upstream”. It will be interesting to see trend of chlorine consumed per Million Liters Day (MLD) and operating costs at a water treatment plant as a function of average TOC/COD/BOD levels at the raw water intake works! I wish such data is collected, analyzed and reported.
The issue is however not just increase in the operating costs. A new dimension of health risk gets introduced. In the process of disinfection of polluted (high TOC) water, several Disinfection By Products (DBPs) are formed. These DBPs can pose significant health risks, especially on occurrence of cancer and lead to substantial medical costs.
You should visit web page of US EPA http://water.epa.gov/drink/contaminants/basicinformation/disinfectionbyproducts.cfm# that provides information on what disinfection byproducts does EPA regulate, how are they formed, and what are their health effects in drinking water at levels above the maximum contaminant level?
Chlorinated DBPs are considered potentially carcinogenic and have been associated with adverse reproductive outcomes following exposure during pregnancy. Tri Halo Methanes (THMs) are the most important group of DBPs.
THMs include chloroform, dichlorobromomethane (DCBM), dibromochloromethane (DBCM) and bromoform (BF). Organic matter in natural water, expressed as TOC, is considered as the dominant THM precursor in drinking water. The World Health Organization (WHO) has set limits on THM. Indian Standard 10500 also specifies thresholds to THMs in drinking water.
Figures (a), (b), (c) and (d) show various relationships between COD, TOC, Chlorine dose, THMs and health risks.
Figure 2 below shows the “dynamics” of TOC and THMs from upstream to downstream.
How much do we know about the levels of THM in our drinking water?
Research carried out in India on formation of THMs is very limited and has shown mixed results when water was analyzed at the water treatment plants, at the reservoirs and in the swimming pools. There is a need to conduct THM monitoring systematically over a year, on a national basis and at all major water treatment plants. We need to understand and assess the cause that leads to generation of the THMs. Here, wastewater inventories at the upstream will also need to be carried out. Occurrence of cancer instances, especially of the bladder will also need to be looked at through community health surveys. Results of this field work must be shared with the public with a preventive and corrective plan launched. We need to seriously tackle pollution at the upstream, optimize operation of chlorine based disinfection and even think of substitutes to chlorine.
We could perhaps develop a Risk Index or a Score Card for a water treatment works based on potential generation of THMs and pay for water accordingly. If the risk index is high then the water treatment plant will need to be compensated by the wastewater dischargers upstream. The Regulator will have an important role to play by slapping additional fines.
Indeed, we must address the nexus of Pollution upstream and By Products downstream. We also need to raise the question who should pay? For this, the Regulators, Wastewater dischargers upstream, Water Treatment Plant operators downstream, Medical practioners and the Community must talk and come up a rounded solution. We need to look at the problem in 3600 and not in a narrow perspective of mere compliance to in-stream BOD and COD standards.
Cover image sourced from http://www.tpomag.com/editorial/2013/01/a_sparkling_legacy