Tonderayi S. Matambo (Editor) – Associate Professor, University of South Africa, South Africa
Grace N. Ijoma (Editor) – Postdoctoral Fellow/Researcher, University of South Africa, South Africa

Series: Environmental Research Advances

BISAC: SCI026000

Human activities extensively contribute to various types of wastewater. These include domestic, industrial, agricultural and storm water. Depending on the waste, they consist of organic material, inorganic material, nitrates, phosphates and metals. Conventional methods of wastewater treatment incorporate various stages, screening, a biological treatment process involving the formation of coagulates, gravity separator, and a clarifier to remove remaining suspended solids. This is further treated using oxidizing and disinfecting agents to reduce the biochemical oxygen demand (BOD) levels. Chemicals such as chlorine are added to bring the water quality to required levels. Biological treatment systems currently being employed in industry include membrane bioreactor (MBR) and moving bed bioreactor (MBBR), which are followed by ultrafiltration treatment.

Conventional wastewater treatment methods are expensive. One technology that has been researched and found to have potential are constructed wetlands (CWs). Wetlands are ecosystems that consist of a variety of biodiversity of aquatic plants and microorganisms. Wetlands act like filters that break down waste from water. Constructed wetlands are engineered wetlands that mimic natural wetlands that consist of a gravel bed through which wastewater flows. As the wastewater passes through the gravel it encounters a natural system comprising of microbiological activity, phytoremediation and filtration. Indigenous plant species are used to promote biodiversity. Plants and bacteria utilize certain components of these pollutants and in this way clean up the wastewater. Due to this ability of remediating polluted water, they are usually used in both secondary and tertiary treatment processes. This is the case in constructed wetlands and wastewater treatment plants. Often this remediation is achieved through biosorption and sequestration mechanisms and sometimes biomineralization may occur if these pollutants can be incorporated into biochemical pathways. But overall the COD is significantly reduced in the polluted water. The biochemical route may involve plant and microbial participation in the carbon, nitrogen and sulphur cycles by transforming them and releasing them into the atmosphere.

Natural wetlands, constructed wetlands, and wastewater treatment plants fail in time and this is demonstrated by clogging, which occurs as a result of build-up of sediments and precipitates in wetland beds, thus constituting reductions in physical media permeability and hydraulic conductivity of water. In natural wetlands it is associated with the aging process of the water body. However, this is more rapidly indicated in constructed wetlands causing a system failure, because of organic and inorganic matter settling at the bottom, thereby slowly filling up the system and causing a decrease in dissolved oxygen levels as decomposition takes place. This phenomenon can be referred to as eutrophication. Normally, clogging and sludge bulking in wetlands can be likened to the phenomenon of eutrophication, sometimes with associated foaming in conventional wastewater treatment. Clogging not only contributes to systems failure in natural and constructed wetlands but it also reduces operational efficiency reducing the ability of resident organisms to biodegrade pollutants. This book will provide a holistic overview of natural wetlands and possible reasons for system failure in constructed wetlands.