Role of Desludging of septic tanks in Environmental conservation and scope for economic benefits

Draft- not to be quoted

Role of Desludging of septic tanks in Environmental conservation and scope for economic benefits

Abstract

Improving global access to clean drinking water and safe sanitation is one of the least expensive and most effective means to improve public health and save lives. The concept of clean water and safe sanitation as essential to health is not a novel idea. However, the sanitation situations in developing countries like India are still in worst conditions. Millions of households rely on pit latrines for sanitation and when a pit fills up, emptying is often the only viable option. Despite the development of several technologies, their limitations have underlined the need for further improvements. Creating a solution that is able to access densely populated settlements, narrow roads, efficiently empty dense sludge and dispose of them at an appropriate location is a difficult task. This paper is a preliminary attempt to understand the basics of septic tanks, problems involved in maintenance of septic tank or pits. It also presents the process of desludging and post desludging of septic tanks. 

Keywords: Septic tank, desludging, sanitation, India, developing countries

Introduction

Global figures that describe the lack of water and sanitation services are alarming. More than 1.1 billion people do not have access to improved drinking water supplies. Lack of sanitation is an even larger problem; an estimated 2.6 billion individuals live without improved services. “Improved access” to water and sanitation may, but does not necessarily, represent access to water or sanitation services that meet international engineering and health standards, such as those set forth by World Health Organization (WHO) Guidelines for Drinking Water Quality. Rather, the term “improved access” usually represents households that obtain water from sources that are superior to traditional, unprotected ones. Sources that meet the definition of improved water include a household connection, borehole, protected dug well, protected spring, or rainwater collection. Connection to a public sewer or septic system or use of ventilated pit latrines and some simple pit latrines qualify as improved sanitation (WHO 2004).

According to NSSO 2008-2009, about 49 thousand slums were estimated to be in existence in urban India. The sanitary conditions in the slums in terms of latrine facility during these years
showed considerable improvement since 2002. Latrines with septic tanks (or similar facility) were available in 68% notified and 47% non-notified slums (up from 66% and 35% respectively in 2002). At the other extreme, 10% notified and 20% non-notified slums (down from 17% and 51% in 2002) did not have any latrine facility at all (NSSO 2009).

Census 2011 results have indicated that nearly 17 million urban households (more than 20 percent of the total 79 million urban households) suffer from inadequate sanitation. According to the report of the Central Pollution Control Board (2009), the estimated sewage generation from Class - I Cities and Class - II Towns is 38254.82 million liters per day (MLD) out of which only 11787.38 MLD (30%) is being treated and the remaining is disposed into the water bodies without any treatment due to which three-fourths of surface water resources are polluted.

Poor wastewater management coupled with lack of sanitation facilities has aggravated the sanitation challenges in developing countries. The inappropriate disposal of municipal wastewater poses a great threat to the environment and public health because human excreta are responsible of the transmission of several infectious diseases which affect millions of people in the world. According to the WHO, the major part of all illness in developing countries is caused by water and sanitation related diseases (WHO 2010; Montgomery and Elimelech 2007). Sewage and effluent can contain a variety of human disease-causing microorganisms and parasites. Disease can be spread to humans from this material by direct contact or indirectly by consumption of contaminated food or water. The safe disposal of sewage and effluent is therefore essential to protect the health of the community. Against to this background this paper is an attempt to understand the consequences of septic tank/ pits management in Indian urban and peri - urban areas. This paper is having sections viz basic concepts of septic tanks, maintenance of septic tanks, problems in maintenance of septic tanks, desludging process and post desludging process followed by concluding remarks.

Septic Tanks

This section gives a brief note on the structure and functioning of septic tanks. Septic tanks are the primary source of septage generation. Septic tanks are watertight sited below ground level which receive excreta and freshwater from flush toilets and other domestic sullage (collectively known as wastewater). A septic tank for the treatment of household wastewater is a horizontal continuous flow type sedimentation tank. This functions as a settling tank and digestion unit. The solids in the wastewater settle to the bottom of the tank where they undergo anaerobic degradation along with the organic matter in the wastewater. Studies have shown that only about 30% of the settled solids are anaerobically digested in the septic tank (CPHEEO 1993).

Hence, there will be a buildup of solids in the settling tank, which if not removed frequently will affect the performance of the settling tank. Oil and grease and other lighter material will rise and float on the surface of the liquid. This is referred to as scum. The tank is designed that the sludge and scum together occupy about ½ to 2/3^rd of the tank’s capacity (prior to de-sludging). Studies have established that a liquid retention of time of 24 hours ensures quiescent conditions for effective settling of suspended solids. Considering, the volume required for sludge and scum, septic tanks are designed with liquid holding times of 2 days (CPHEEO 1993).

A septic tank is generally followed by a soak-away pit to disperse the effluent into the ground. The sludge settled at the bottom and the scum at the top of the sewage is allowed to remain in the tank for several months during which they are decomposed by bacteria through anaerobic digestion (CPHEEO 1993).

Maintenance of septic tank systems

The major function of a septic tank is to separate solids, grease and oils out of the wastewater before it enters the drainage receptacles. When a septic tank system is correctly installed and maintained, it should work effectively for many years.

If the septic tanks accumulate too much sludge and scum, the effective volume of the tank is reduced which in turn reduces the time for separation to take place. This means not all the solids, grease and oils will separate and will pass out of the septic tanks and into the drainage receptacles. This will clog the soil surrounding the drainage receptacle and should be avoided.

To prevent this from happening, it is necessary to have the septic tanks desludged (pumped out) regularly. Desludging requires that a licensed liquid waste contractor be engaged to open the septic tanks and pump out the contents. The desirable frequency of desludging is dependent on the number of people contributing to the wastewater load. As a guide, every eight years for a two person household, every four years for a four-person household and more often for households with greater numbers, is recommended. Alternating drainage receptacles should be switched regularly (annually). This requires that the diverter box be opened and the effluent flow handle turned to the appropriate position.

Major Problems in maintenance of Septic tanks

Failure of septic tank systems generally means failure of the drainage receptacles. Failure is most commonly seen in older systems constructed with a single non alternating drainage receptacle, particularly if large volumes of water are frequently used, or in systems that have not been correctly installed or maintained. In systems that have been used for some time, the soil surrounding the drainage receptacle can begin to clog up. Effluent is less able to freely soak into the surrounding soil and begins to accumulate in the drainage receptacle until it fills up.

When this happens, the following can occur:

Ø  Sewage begins to back up into household pipes. This is commonly first noticed when household fixtures like toilet won’t drain away easily, or you notice sewage overflowing from a small grated pipe located outside the building called an overflow relief disconnector gully.

Ø  The ground becomes soggy around the drainage receptacle and effluent may seep from the soil to the surface. This smells unpleasant and is a health risk.

Desludging Process:

Sludge production is a natural process which happens in all correctly operating sewage treatment systems and de-sludging is crucial to the continued correct and satisfactory performance of sewage treatment plants. In other words, sludge is the solid matter produced in and by all sewage treatment systems. It consists of inert solids and biological matter. The inert solids come from the solid matter flushed into the septic tank from the toilet. Some of the biological matter is in the wastewater but most is produced as a consequence of the natural processes (growth of micro-organisms) which are an essential part of the operation and actions of the septic tank as it purifies the wastewater (sewage).

A person should stop using a pit latrine when it is almost full. There are two options: one, stop using the latrine and construct a new one or; two, empty the contents and reuse it (Pickford and Shaw 1997). Often, the lack of available space or costs of constructing a new latrine superstructure and pit means that pit emptying may be the only practical alternative (Muller and Rijnsburger 1994). Neglecting pit emptying requirements can have serious health and environment consequences.

Figure 1: Desludging Process of Septic Tank

Source: http://www.themimu.info/emergencies/wash-cluster

It is also important to notice that, disposal of sewage sludge shall have a legal and social obligation for its safe disposal, called the ‘Duty of Care’. The duty of care requires you to take all reasonable steps to ensure that the waste is safely disposed of by an authorized person. It applies to everyone involved in handling wastes including sewage sludge, from the person who ‘produces’ it to the person who finally disposes of it or uses the material.

Post desludging:

Conventional sanitation systems dispose of around 50 million tons of fertilizer into the environment, with an equivalent market value of around $15 billion (Werner 2004; Rosemarin et al 2008; Rosemarin et al 2011).  At the same time, unsustainable agricultural practices lead to soil degradation and depletion of nutrients in the soil. Mineral fertilizers on which modern agriculture practices depend upon are new-renewable resources. It is estimated that there will not be sufficient phosphorus supplies from mining to meet agricultural demand within 30 to 40 years and from a global perspective, 38% is of agricultural land has already been degraded since the end of World Water II (Scherr 1999).

Wastewater streams also contain valuable nutrients, such as nitrogen and phosphorous. The fertilizing equivalent of excreta is nearly sufficient for a person to grow its own food (Drangert 1998). Each day, every person on the planet excretes approximately 10-12 g of Nitrogen, 2 g of Phosphorus and 3 g of Potassium. Most of the organic matter is contained in the faeces, while most of the nitrogen (70 to 80 per cent) and potassium are contained in urine (Strauss 2000). The organic matter contained in faeces and organic wastes also plays an important role in soil fertility improvement, and the use of nutrient-rich water for agriculture and landscaping may lead to a reduction or elimination of fertilizer applications. Therefore desludging is not only environmental friendly solution in sludge management but also generate income.

Once the sludge is collected it has to be disposed of. Therefore disposal must be considered in parallel with pit emptying technologies. Final disposal of solid wastes, including sludge, is one of the most neglected infrastructures in developing countries. The provision of inadequate facilities may result in indiscriminate or illegal disposal of sludge to rivers, open drains, the sea or any open space (WUP 2003), particularly if the emptying technology does not possess appropriate haulage capacity for long distances and government systems are not supportive. It also requires new interventions towards septage management and next steps towards waste to energy.

Conclusion

The challenges in pit emptying are complex, compounded by the variable and often difficult conditions in which emptying technologies must operate. As more innovations are tested and improved, progress can be made towards a satisfactory solution. However, this will take time as some difficulties are not identified until technologies have been used for a sufficient period. There may also be scope to investigate novel ways of emptying pits instead of simply attempting to adapt current technologies. There is also a scope to draw lessons from research done in the management of municipal solid waste. This should always be carried out with a system of haulage and disposal in mind.

References:

Central Pollution Control Board (CPCB). (2009). Status of water supply, wastewater generation and treatment in Class I cities and Class II towns of India. Series: CUPS/70/2009-10. Central Pollution Control Board, New Delhi, India.

Central Public Health and Environmental Engineering Organization (CPHEEO) (1993), Manual on Sewerage and Sewage Treatment, 2^nd  Edition, Ministry of Urban Development, New Delhi, India

Drangert, J.O. (1998). Fighting the Urine Blindness to Provide More Sanitation Options. Water South Africa, Vol. 24, No. 2, April.

Montgomery, M.A. and M. Elimelech (2007) Water and Sanitation in Developing Countries: Including Health in the Equation. Environmental Science & Technology, 41, 17-24. http://dx.doi.org/10.1021/es072435t  

Muller, M. & Rijnsburger, J. (1994) MAPET: A neighbourhood based pit emptying service with locally manufactured handpump equipment in Dar es Salaam, Tanzania. WASTE.

NSS Report no. 534 on “Some Characteristics of Urban Slums 2008 http://indiafacts.in/poverty/slums-in-india/ accessed on 18^th November 2014 @11.13pm

Organization, W.H. (2010) Water, Sanitation and Hygiene Links to Health Facts and Figures-Updated November 2004. WHO, Geneva.

Pickford, J. & Shaw, R. (1997) Technical Brief No. 54: Emptying latrine pits. Waterlines, 16 (2), 15 – 18.

Rosemarin, A., Ekane, N., Caldwell, I., Kvarnström, E., McConville, J., Ruben, C. and Fogde, M. (2008). Pathways for Sustainable Sanitation: Achieving the Millennium Development Goals. Stockholm Environment Institute. IWA Publishing, London

Rosemarin, A., Schröder, J., Dagerskog, L., Cordell, D., and Smit, B.: Future supply of phosphorus in agriculture and the need to maximise efficiency of use and reuse, IFD proceedings 685, Leek, United Kingdom, 2011.

Scherr, S.J. 1999. Soil degradation: A threat to developing country food security in 2020? Food, Agriculture and the Environment Discussion Paper 27. Washington DC. IFPRI.

Strauss, M., Heinss, U., Montangero, A. (2000). On-site sanitation: when the pits are full planning for resource protection in faecal sludge management. In: Proceedings, International Conference on Resolving Conflicts between drinking Water Demand and Pressures from Society’s Wastes (Chorus et al., editors). Bad Elster, Germany, 24-28 November.

Werner. C., Avendaño V., Demsat S., Eicher I., Hernandez L., Jung C., Kraus S., Lacayo I., Neupane K., Rabiega A. & Wafler M. (2004). Ecosan – closing the loop. Proc. 2^nd International Symposium on ecological sanitation, Lübeck Apr. 7-11. 2003, GTZ, Esch - born, Germany, 1004p.ISBN 3-00-012791-7.

WHO/UNICEF, (2004). Meeting the MDG Drinking Water and Sanitation Target: A Mid-Term Assessment of Progress; WHO: Geneva.

WUP (2003) Better Water and Sanitation for the Urban Poor. Kenya, European Communities and Water Utility Partnership

 Annexure 1: Summary of Sanitation status in India (survey from different agencies)

India		SANITATION
		URBAN								TOTAL
		Sewer connection		Total improved (incl shared)		Shared		Open defecation		Sewer connection		Total improved (incl shared)		Shared		Open defecation
Source	Year	Used in ests.	Not used	Used in ests.	Not used	Used in ests.	Not used	Used in ests.	Not used	Used in ests.	Not used	Used in ests.	Not used	Used in ests.	Not used	Used in ests.	Not used
Census	1991
Demographic and Health Survey	1993	29.5		70.0				24.1		8.4		26.6				70.6
National Sample Survey	1993	28.5		65.3				30.6		8.1		25.8				71.3
National Sample Survey	1996	29.6		73.4				23.0		8.4		29.4				67.9
Demographic and Health Survey	1999	28.2		75.9		26.1		19.3		8.3		32.7		16.0		64.1
Multiple Indicator Cluster Survey	2000	25.3		72.9				22.0		7.6		31.5				64.8
National Census	2001	20.3		63.8				26.3		6.1		30.7				63.6
National Sample Survey 2002	2002			74.0				17.9				32.1				59.8
World Health Survey	2003		34.3		84.7				13.6		11.7		37.7				59.8
District Level Household Survey 2002-2004	2003			75.0		18.3			20.2			32.9		13.2
Demographic and Health Survey	2006	28.3		77.5		29.2		17.0		8.9		39.3		23.0		57.1
District Level Health Survey	2008			74.4				19.2				40.9				51.7
Study on global aging and adult health, WHO	2008	17.9		69.5		25.6			27.1	5.8		40.2		20.2
National Sample Survey 2008 - 2009	2009			82.7				11.3				43.6				48.7
Coverage Evaluation Survey	2009				84.4				12.9				52.7				44.8
Census	2011	32.7		85.0				12.6		11.7		46.9				50.2