Natural wastewater treatment- large-scale treatment plants

Abstract

Large scale natural wastewater treatment plants are used more and more worldwide. The most common types of natural treatment systems are the con-structed wetlands serving as secondary treatment steps in the wastewater treatment facilities. The aim of this work was to make a literature review on the application of natural treatment units in large scale wastewater treatment. In this work several large-scale wetlands and other different types of natural wastewater treatment plants in use are presented. Additionally, the possibilities of using natural treatment units in China are considered.

This study showed that the main natural techniques applied in large scale are artificial shallow basin wetlands, floating treatment wetlands, large scale off-shore photobioreactors and settling basins. Different wetlands have their own benefits for the surroundings, but the varying efficiency is a general problem. For the natural wastewater treatment plant, the removal for main pollutants like BOD, COD or phosphorus are well enough, but there is still long way to be efficient for other pollutants. Natural treatment systems are also sensitive to variation in the pollutants. Mixing of different types of wastewater causes mixing of the pollutants that might compromise the purification. For example, a wetland originally designed for school, hospital, and agriculture wastewater, cannot deal with industrial wastewaters. Antibiotic resistant genes appearing in hospital wastewaters treated in wetlands pose a threat to human health. Natural treatment plants are not the best solution for wastewater treatment in China, mostly because urbanization and high transportation costs.