The performance of constructed wetlands for, wastewater treatment: a case study of Splash wetland in Nairobi Kenya

Abstract

Abstract:The performance of a constructed wetland for wastewater treatment was examined for four months (December 1995 to March 1996. The study area, hereby referred to as the Splash wetland, is approximately 0Ð5 ha, and is located in the southern part of Nairobi city. Splash wetland continuously receives domestic sewage from two busy restaurants. Treated wastewater is recycled for re-use for various purposes in the restaurants. Both wet and dry season data were analysed with a view of determining the impact of seasonal variation on the system performance. The physical and chemical properties of water were measured at a common intake and at series of seven other points established along the wetland gradient and at the outlet where the water is collected and pumped for re-use at the restaurants. The physico-chemical characteristics of the wastewater changed significantly as the wastewater flowed through the respective wetland cells. A comparison of wastewater influent versus the effluent from the wetland revealed the system's apparent success in water treatment, especially in pH modification, removal of suspended solids, organic load and nutrients mean influent pH D 5Ð7 š 0Ð5, mean effluent pH 7Ð7 š 0Ð3; mean influent BOD 5 D 1603Ð0 š 397Ð6 mg/l, mean effluent BOD 5 D 15Ð1 š 2Ð5 mg/l; mean influent COD D 3749Ð8 š 206Ð8 mg/l, mean effluent COD D 95Ð6 š 7Ð2 mg/l; mean influent TSS D 195Ð4 š 58Ð7 mg/l, mean effluent TSS D 4Ð7 š 1Ð9 mg/l. As the wastewater flowed through the wetland system dissolved free and saline ammonia, NH 4 C , decreased from 14Ð6 š 4Ð1 mg/l to undetectable levels at the outlet. Dissolved oxygen increased progressively through the wetland system. Analysis of the data available did not reveal temporal variation in the system's performance. However, significant spatial variation was evident as the wetland removed most of the common pollutants and considerably improved the quality of the water, making it safe for re-use at the restaurants.

The role of wetlands in the changing ecophysiology and distribution of plant species: a comprehensive review

“…Wetlands are regulators of water quantity and water quality (Nzengy'a and Wishitemi, 2001). Natural and constructed wetlands can remove large amounts of nutrients and suspended solids from surface water flowing through them (Beadle et al, 2004;Huang and Pant, 2009).Wetlands can remove and store large amounts of N and later released to the ecosystems mostly in organic forms.…”

“…Natural and constructed wetlands can remove large amounts of nutrients and suspended solids from surface water flowing through them (Beadle et al, 2004;Huang and Pant, 2009).Wetlands can remove and store large amounts of N and later released to the ecosystems mostly in organic forms. Previous studies in Kenya have revealed that Cyperus papyrus swamps are efficient in nutrient removal for the purpose of wastewater quality improvement (Nzengy'a and Wishitemi, 2001). Nitrogen retention in the wetlands occurs through a variety of mechanisms including filtration, adsorption, ion exchange, biological assimilation, and denitrification (Lee and Caporn, 1998;Huang and Pant, 2009).…”

“…Nitrate uptake by aquatic plants acting as, 'temporary' sinks, may be important in young wetlands or trivial in mature vegetation stands (Huang and Pant, 2009). Constructed freshwater wetland can provide reliable tertiary treatment of municipal wastewater (Nzengy'a and Wishitemi, 2001). The accomplishment of wetlands in the removal of nutrients, trace metals, organics and pathogens is attributed to diverse wetland processes such as sedimentation, filtration, chemical precipitation, adsorption, microbial interaction and uptake by vegetation (Nzengy'a and Wishitemi, 2001).…”

“…Eutrophication can also be defined as the enrichment of water body with plant nutrients particularly nitrates and phosphates, resulting in the nuisance of algal blooms and aquatic macrophytes (Awange and Ong'ang'a, 2006). Increased concentrations of nutrients through runoff from agricultural land and changes in land use which increase run off contribute to eutrophication (Nzengy'a and Wishitemi, 2001). There are usually two consequences of eutrophication on plant communities: (1) an increase in emergent plant biomass and (2) a decrease in plant species diversity at high production levels (McJannet et al, 1995).…”

“…Constructed wetlands have been successfully used to retain nutrients from treated wastewaters (Gale et al, 1993;Romero et al, 1999). Macrophytes remove pollutants by (i) directly assimilating them into their tissues, (ii) providing a suitable environment for microbial activity and (iii) slowing down water movement flow rates and thereby allowing sedimentation to take place (Nzengy'a and Wishitemi, 2001). Wetlands may be an integral part of integrated riparian management systems and are highly efficient at denitrification because of their large quantities of organic sediments and decaying plant material (Schultz et al, 1994).…”