A solid life-cycle approach to control the content of sludge in wastewate

E.K. Mohanraj (7221449)

K. Krishnamurthy (7221455)

S. Anandakumar (7221452)

English

Loughborough University Institutional Repository

28th WEDC Conference Kolkata (Calcutta), India, 2002 SUSTAINABLE ENVIRONMENTAL SANITATION AND WATER SERVICES A Solid Life-Cycle Approach to Control. The Content of Sludge in Waste Water E. K. Mobanraj, S. Ananoakumar & K. Krisbnamurtb�, InoiaEffective wastewater treatment remains a priority on the wish lists of many Indian environmentalists. But this wish remains unfulfilled as the water bodies downstream from several major Indian cities (such as Delhi, Mumbai, Kolkatta, Chennai & Hyderabad) continue to receive untreated sewage. The ingredients of this noxious soup include human waste along with other unsavoury items flushed down toilets and washed down drains, such as pharmaceutical products. They also include effluents from business and industrial operations and, in many cases where sanitary and storm sewers are combined, runoff from urban areas. The latter two sources may con tribute heavy metals, pesticides (which includes a whole host of constituent compounds), polyaromatic hydrocarbons (PAHs), and other organic compounds. The best bet to reduce the environmental burden of the sewage "life-cycle" as well as environmental impacts of land application is a combination of upstream control over what is allowed to become part of the sewage sludge with downstream best practices to manage final disposition as a land-applied "biosolid". Life-cycle inventories rely on a simple accounting of physical units or, as engineers refer to them, "mass balance". For instance, when dental amalgams containing mercury are used, the bulk of the mercury stays within the amalgam (the filling), a very small portion is ingested by the patient (some is passed), and the remainder is washed down the drain when the patient washes their mouth out. The portion passed and the portion washed down the drain end up at the sewage treatment plant of which some remains in the sewage sludge and the balance is discharged to the receiving water body. With a heavy­metals management program at the sewage plant being prohibitively expensive to build and operate (and according to experts in the field, technologically unproven), the simple solution becomes pollution prevention at the dentist's office. That is, the substitution of the use of mercury based dental amalgams with the use of composite materials. Irrespective of whatever is subjectively considered "acceptable" for land application, the ongoing reduction of metals in sewer loadings can only increase pubiic confidence in the practice of regulated land application of biosolids. Of even greater importance, reducing the loadings of these constituents to sewers means reducing the portion going to receiving water bodies. When heavy rains occur the system overflows, sending raw sewage and urban runoff into receiving water bodies. Urban runoff is comprised of rainwater and a host of chemicals that wash off of parking lots, industrial parks and roads. These include wearing automobile parts ( chromium, cadmium, copper, lead, and arsenic), automotive emissions (PAHs, used motor oil, spilled diesel and coolant), pesticides and herbicides, and solvents and coatings (from painting and metal processing). Having taken these upstream steps, the resulting sewage sludge is freer of many of the heavy metals and organic compounds than it would have been otherwise. Nevertheless it remains noxious. Untreated human waste contains bacteria, viruses and other pathogens that must be treated fully to render the resulting biosolid virtually pathogen inert. Introduction I a typical metropolitan region, an abandoned canal ditch is used as a chemical dumping site for over thirty years, then closed. Several years afterward, homes are constructed adjacent to the site and an elementary school is opened. Two decades later, residents complain of noxious basement odors. It becomes evident that the serious health hazard exists, the result of chemical waste disposal begun more than half century earlier. The current high level of understanding of the mechanisms applied to waste water treatment has resulted from the collaboration of microbiologists, biochemists, sanitary engineers and chemical engineers. This collaboration has led to the construction of many technically advanced and highly successful sewage - treatment plants. These plants generally use aerobic processes for the degradation and mineralization of the organic compounds in the sewage and anerobic processes for the stabilization and mineralization of sludges, although, and conversley, anaerobic systems are also used for liquid waste water treatment, particularly for the treatment of strong organic industrial waste waters, and sludges are stabilized aerobically. Any change in the composition of waste, which often includes polluting materials like heavy metals or toxic chemicals, may take necessary development of new, more efficient treatment processes in respect of conversion MOHANRAJ et. al. Table - 1 Metals in domestic sewage sludge (mg/kg dry solids) Type of sludge Dry Solids{%) Cd Cr Raw sludge Ex. 1 1.9 20 90 Raw sludge Ex. 2 4.9 20 42 Digested sludge 2.7 20 403 Estimating the fate of Hazardous Chemicals A basic question in our evaluation of hazardous wastes in the environment is that of the implications for human health. One problem in predicting the fate of toxic substances - or of any pollutant, for that matter -is that the science dealing with environment pollution is so young, having surfaced formally only within the last two decades. The state of our knowledge, though growing daily, is limited. Unfortunately, decisions regarding regulation of environmental pollution need to be made today. When making decisions based on limited information, we must exercise caution. A common tool used to make predictions is the mathematical model, generally a series of equations that attempt to describe the characteristics and response of some physical system. Mathematical models are used in many sciences. In economics, they are used to predict trends in market activity, the occurrence of recession or productive periods, and the like. In meteorology, they are used for prediction of short - term weather conditions as well as long- term climatological changes. In the environmental sciences, mathematical models can be used to predict the transport and fate of pollutants. Such models need not be complex sets of equations, incomprehensible to the average man, although in some cases these may be necessary. The advantage of mathematical models is that they enable the scientist and engineer to integrate in a consolidated frame work all the various reactions that proceed simultaneously, affecting the concentrations of various pollutants. The Metal Content of Sludges A disadvantages of sewage sludge is that it may contain appreciable concentrations of potentially toxic materials. The best-documented toxins are the heavy metals. Since the new Water Act of 1973, more rigorous consent conditions have been imposed by the water authorities on industrial discharges to sewar and in many cases the concentrations of metals in sludges has fallen by over 50 percent. Additional improvements have been brought about by the recession of old heavy industry. There is, therefore, greater potential for the reuse of sludge as a fertilizer. At present it is used on only 1.25 percent of the land used for agricultural purposes in the Cu Fe Pb Ni Zn 315 13814 300 15 871 169 6651 206 15 568 605 19355 454 81 1411 UK. Most data on phytotoxicity relate to zinc, copper and nickel; their effects seem to be additive. To cater for the most sensitive crops it is assumed that copper is twice as toxic as zinc, nickel eight times as toxic and boron 150 times more toxic than zinc. Cadmium, lead and chromium cause problems for the consumer rather than having a direct effect on plant growth. Cadmium accumulates in the leaves of plants and additions are restricted to 5 kg/ha per year. Lead and chromium are · less toxic since they are not taken into the edible part ofthe plant. Normally, totally domestic sewages have lowconcentrations of heavy metals, but they may containappreciable quantities of zinc from costemics and pipework. Table - 1 above shows the metal content of sometypical waste water sludges.Conclusion Waste water should be properly treated before it returns to the natural environment, or otherwise it will cause so many health hazards to the society. Treated water or restored water can be consi9ered as a safe measure for reuse. Proper planning must be emphasized for reuse of polluted water for other than drinking purposes. The major portion of water used by the mankind is only for secondary purposes. So, justification is made economically to produce significant savings by reuse of treated water. Reference 1. John M. Sidwick and Roger S. Holdom, Biotechnology ofWaste Treatment and Exploitation, 1987, Ellis Horwood Ltd.,Market Cross House, Chichester, West Sussex, England.2. Herman Korean and Michael Bisesi, Handbook ofEnvironmental Health and Safety, 1999, Jaico PublishingHouse, Mumbai.3. Michael D. Lee and Jan Teun Visscher, Water Harvesting: Aguide for planners and project managers, IRC InternationalWater and Sanitation Centre, The Hague, The Netherlands,1992.E. K. MOHANRAJ, S. ANANDAKUMAR, K. KRISHNAMURTHY; Faculty in Civil Engineering, Kongu Engineering College, Perundurai-638 052, Erode Dist. Tamil Nadu. 

A solid life-cycle approach to control the content of sludge in wastewater

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A solid life-cycle approach to control the content of sludge in wastewater

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