Composition of human excreta — a case study from Southern Thailand

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Abstract

In Thailand, human excreta might be recycled into agricultural soils as a supplement to commercial fertiliser and thereby enrich the general fertility of the soils. However, for Thailand an adequate knowledge of the quality of human excreta, in order to assess its fertiliser potential, is not available. A literature survey revealed only very limited information of the chemical composition and generation rate of human excreta in South East Asia. Data from other parts of the world also lacked specific information on collection and analytical methods, or the studies were typically 20–30 years old. In the present study the composition of human excreta has been studied in three case study areas in Southern Thailand: Kuan Lang, Phattalung and Prik. The inhabitants of the three areas represent people of Southern Thailand by age, sex, occupation, religion and type of residence. Human excreta was collected and stored for 1 week from five persons in each area, who each had their own toilet and collection bucket. In parallel, a septic tank at the Observation and Protection (O&P) Centre of Songkhla (a boys prison institution) adjacent to the three study areas was used as a daily sampling point, to obtain data on average amounts of human excreta and chemical composition. Information on average values of generation rate and chemical composition was obtained as well as inter-human variation. However, no significant variation was found between the results for human excreta at the O&P Centre or from the 15 individuals. Furthermore, there was no significant influence of age, sex, occupation or religion on the chemical composition. The only significant variation was that the older people excreted larger amounts of total wet matter than the younger, which could be due to a higher water intake, in order to reduce the risk of constipation. The generation rate found was 0.6–1.2 l urine/cap/day and 120–400 g wet faeces/cap/day. The generation rate of the elements in the excreta was 7.6–7.9 g N/cap/day, 1.6–1.7 g P/cap/day, 1.8–2.7 g K/cap/day, 1.0–1.1 g S/cap/day, 0.75–1.5 g Ca/cap/day, 0.25–0.4 g Mg/cap/day, 9–16 mg Zn/cap/day, 1.4–1.5 mg Cu/cap/day, 0.3 mg Ni/cap/day, 0.02–0.03 mg Cd/cap/day, 0.07–0.14 mg Pb/cap/day, 0.01 mg Hg/cap/day and 0.8–1.1 mg B/cap/day. The metals (Ca, Mg, Zn, Cu, Ni, Cd, Pb, Hg) are mainly excreted via the faeces and the remaining elements (N, P, K, S, B) are mainly excreted via the urine. It can be concluded that human excreta constitutes a large fertiliser resource, which presently is not utilised in Thailand.

Introduction

Food is produced directly or indirectly from nutrients in soil and soil–water taken up into plants and after harvest and transport to human settlements they are consumed. Apart from a minor fraction, which is accumulated in the human body, the nutrients end up either in human excreta, solid waste or grey wastewater. Schouw et al. (2001) reported that biodegradable solid waste and wastewater are rarely recycled in Thailand, however, they do constitute a large nutrient potential. In the past the Thai people used to urinate and defecate directly on the agricultural areas. Development brought along toilets where human excreta typically are stored in a subsurface concrete container with an open bottom and with an overflow pipe to a drainage pit. The solid fraction settles in the tank. The liquid leaks out of the container through the bottom or through the overflow pipe, when the surrounding soil is clogged. The container is continuously drained for nutrients and becomes filled up with solids. Every 5–10 years the private households hire a sludge suction truck to empty the container for solids, which are then disposed off at landfill sites or at abandoned areas inside or outside human settlements. Consequently most nutrients in excreta are lost to the surrounding subsoil and water bodies.

Nutrients enter a one-way flow from the soil via wastes to various water bodies. As a consequence it has been reported that presently Thailand and other Asian countries are facing the problem of nutrient depletion in their agricultural soils (Tandon, 1995, Craswell and Karjalainen, 1990)

This problem increases when the urban population, which is currently not recycling their waste, increases. In 1995, 20% of Thailand's 60-million people were living in urban areas and since then the annual urban growth has been 2.8% (UNFPA, 2000). In order to feed this increasing urban population the agricultural sector needs to increase food production. However, increasing the crop yield may often be constrained by the fact that most soils are depleted of nutrients. Therefore, in Thailand recycling of precious nutrients in urban waste is a sustainable supplement to fertilisers. However, there is a lack of general knowledge about the elemental characteristic of human waste and thereby knowledge about the potential fertiliser value of this waste. During the last 25 years only few studies have been made on the quantities and composition of human excreta. These are apparently, either of older dates (Hansen and Tjell, 1979) or the details on the collection procedures are lacking (Polprasert et al., 1981).

The objective of this present paper is to determine the human nutrition intake and load of heavy metals via excreta and to assess human excreta as a fertiliser in the Asian region. Focus is upon the generation rate and chemical composition of human excreta (urine and faeces) in three case study areas in Southern Thailand. Comparisons are made between individual test persons, average values from a large Thai institution and previous studies on human excreta.

Section snippets

Survey sites and study population

The case study areas are Prik, Kuan Lang and Muang Phattalung in the Southern part of Thailand (Fig. 1). The populations of the three areas form the basis of the present study. The areas represent different forms of human settlement in terms of sizes, population density, occupation pattern, religion and industrial and commercial activities (Table 1). Prik is situated near the Malaysian border and represents densely populated rural villages. Kuan Lang is situated near the largest city in

Excreta quantity

The excreta generation rate was determined by collecting the total amount of excreta from 15 test persons (Table 5). The excreta rate ranged from 730 to 1530 g wet matter/cap/day with a dry matter content of 50–87 g dry matter/cap/day. The amount of urine and faeces was, according to the three additional test persons, 0.6–1.2 l urine/cap/day and 120–400 g faeces/cap/day. Even though the test persons guaranteed that only the test toilet was used during the experimental week, it cannot be totally

Conclusion

Human excreta constitutes a large nutrient resource and could beneficially be handled in a more sustainable way than in the present systems in Thailand. In the study presented in this paper the excreta of 15 test persons and the O&P Centre was analysed. It was found that the average generation rate in Thailand is 0.6–1.2 l urine/cap/day and 120–400 g faeces/cap/day. The total excreta generation rate is 730–1530 g wet matter/cap/day. These values are in agreement with earlier studies from Asian

Acknowledgements

We wish to thank the Danish Co-operation for Environment and Development, DANCED and hereunder the Danish University Consortium for Environment and Development, DUCED, for financial support of this study. The Observation and Protection Centre of Songkhla and the test persons of Prik, Phattalung and Kuan Lang are acknowledged for their kind help and willingness to participate in the study. We are also grateful for the keen interest from students and staff at the Faculty of Environmental

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