Constructed Wetlands for Sustainable Wastewater Treatment – Case Studies from Pakistan

Abstract

AbstractLike other countries across the globe, Pakistan’s fresh water resources are stressed by increasing water demand, environmental degradation and the multi-faceted impacts of climate change. Most of the wastewater generated by urban, industrial and agricultural activities is discharged untreated into water bodies thus polluting the vulnerable water resources. The contemporary wastewater treatment systems in most of the developing countries including Pakistan fail to treat wastewater satisfactorily. Reasons for poor treatment include lack of local expertise, high maintenance costs and poor governance. These wastewater treatment systems also require heavy capital investment and high operating and energy costs. Over the years, responsible water management departments in different parts of the world have started diverting to nature-based solutions to mitigate the severe climatic, environmental, economic and societal challenges. Nature-based approaches including constructed wetlands represent more efficient and cost-effective solutions than traditional methods as they are self-operating and self-maintaining. Constructed wetlands (CWs) are passive treatment systems and temperature has a profound impact on the efficiency of CWs; low temperatures reduce the biological activity and decrease the rate of chemical reactions that are important pathways for contaminant transformation and their subsequent removal. CWs have been widely implemented in the developed world where thousands of systems are currently working. These systems are mostly located in geographical locations where temperatures are considerably low. Most of the developing countries including Pakistan are located in regions where temperatures are considerably high and may have arid conditions. This chapter discusses case studies from Pakistan where different types of CW systems have been tested in hot and arid climatic locations. The role of plant-associated microorganisms in the removal of pollutants in CWs is also highlighted. The various aspects of different variants of CWs including free water surface, horizontal flow, vertical flow and floating CWs treating domestic, textile, and produced water from oil and gas field are discussed in this chapter.KeywordsConstructed wetlandsWastewater treatmentDeveloping countriesNature-basedVertical flowHorizontal flowFree water surfaceFloating wetlandsPakistan