Resources and Environment 2014, 4(4): 190-199 DOI: 10.5923/j.re.20140404.02 Characterization of Sewage Sludge Generated from Wastewater Treatment Plants in Swaziland in Relation to Agricultural Uses Joseph S. Mtshali 1 , Ababu T. Tiruneh 1,* , Amos O. Fadiran 2 1 Department of Environmental Health Science, University of Swaziland, P.O.Box 369, Mbabane, Swaziland 2 Department of Chemistry, University of Swaziland, Private bag 04, Kwaluseni, Swaziland Abstract Sewage sludge generated from wastewater treatment plants are being merited greater attention in light of their potential for improving soil properties and for providing important nutrient and trace element supplements that are essential for plant growth. Because of the differences in sludge characteristics among sludges that undergo different levels of treatment as well as the extensive and variable nature of pollutant inputs to wastewater, the fertilizer potential and pollutant risk of sewage sludge intended for agricultural application has to be specifically evaluated for each sludge. Sewage sludge generated from seven wastewater treatment plants in Swaziland were analysed for a range of physico-chemical characteristics including organic matter, nutrients, cation exchange capacity, pH and trace elements. Despite the differences in sludge processing and sludge storage ages, the sludge samples generally show high levels of organic matter, nutrients and trace elements needed for plant growth. The potential risk of heavy metal toxicity was evaluated by comparing the levels of heavy metals in the sludge samples with widely quoted and well known regulatory limits of a number of countries and the levels were found to be within acceptable risk level with respect to agricultural application. The research results indicate a positive outcome for the wastewater treatment plants in Swaziland that currently keep large piles of unused dried sludge within their premises. Keywords Sewage sludge, Nutrient value, Organic fertilizer, Soil amendment, Sludge reuse, Nitrogen, Phosphorus 1. Introduction Sewage sludge is known to be rich in nutrients (nitrogen and phosphorous), organic matter and trace elements that are beneficial for plant growth and better yield [58, 17]. Sewage sludge is also considered a suitable substitute for commercial fertilizers and the use of sewage sludge as a fertilizer decreases the requirement for commercial fertilizers [37]. Commercial fertilizers require large amount of phosphorous whereas phosphorous is known to be a limited resource [54]. Even though the nitrogen available in commercial fertilizers may not be a limited resource, the production of nitrogen fertilizers demand significant amount of energy [52]. The organic carbon in sludge amended soil can increase as far as three fold compared to inorganic fertilizer amended soils [40, 32]. Inorganic fertilizers usually reduce soil pH and increase the rate of soil acidification as well as increasing the percentage of aluminium saturation [36]. The decrease in pH of soils is traced possibly to the ammonium in the fertilizer [30]. In situations where sewage sludge may not contain the * Corresponding author: ababute@gmail.com (Ababu T. Tiruneh) Published online at http://journal.sapub.org/re Copyright © 2014 Scientific & Academic Publishing. All Rights Reserved optimum nutrient ratio for growth, it can be combined with commercial fertilizers [33]. Application of sludge has been observed to improve the physico-chemical and biological properties of soils which in turn facilitates better growth of plants [1, 24]. Sludge increases the humus content of the soil [33]. The porosity, field capacity and wilting point all increase as a result of application of sewage sludge [7]. Organic matter which forms over half of the mass of sewage sludge also improves the physical condition of soils [18]. An increase in organic matter reduces the bulk density, increases aggregate stability, increases water holding capacity of soils and promotes greater water infiltration [21]. Organic matter also influences nutrient storage and turnover, soil biota and diversity as well as vulnerability to erosion, [5]. Infiltration capacity and air recirculation increase in fine textured soils as result of sludge application [12, 46]. By contrast, the increased bulk density of fine textured soils without sludge amendmet causes poor aeration which adversely affects plant growth [10].Macro elements are essential for plants and soil fauna [22]. Treated sewage sludge can enrich soil with macronutrients such as phosphorus, potassium, sulfur, calcium, magnesium and micro nutrients [62]. For example, a macro nutrient imbalance in the form of high exchangeable sodium percentage can cause nutritional disturbances in plants and