Tree-sewage symbiosis for healthy forests and people

The deterioration of surface and groundwater quality in peri-urban areas of many emerging economies such as India, Indonesia, Malaysia, Pakistan and Vietnam is a serious cause for concern. Limited prospects for connections to conventional sewage networks and treatment plants mean that natural treatment based on constructed wetlands and/or vegetative filters has many advantages in terms of accessibility, affordability, low or zero energy requirements and low running costs. Among such approaches, filtering through the root zone of trees can help provide products and services of economic value (e.g. wood, fodder, seeds, oils, medicines). For example, a study from the north of India using fast-growing tree species to treat domestic greywater reduced pollutant loadings by 60-77% and showed net monetary benefits of $86000/hectare after 5 years [1]. Nonetheless, wastewater treatment by trees is not yet widely practiced due to the limited understanding of the efficacy of such systems and how to implement and manage them in real settings.
By addressing gaps in knowledge and barriers to implementation, he PhD project will aim to reduce the instance of waterborne pollution and disease through sustainable plantations of trees. The specific objectives will be to:
1. Develop reliable models for the removal and fate of contaminants in wastewater by the tree root zone using suitable measures and indicators
2. Develop recommendations for the tree species selection, cultivation method, plantation design and irrigation method in representative case studies
3. Understand and quantify the economic value of forestry products obtained. This may include direct benefits such as sale of wood or fodder, as well as external benefits such as carbon sequestration.
4. Understand the safety aspects and perceptions by consumers related to water re-use following root-zone purification and possible supplementary treatments (e.g. UV treatment, chlorination).
5. Understand how irrigation by wastewater can support and maintain forested landscapes, how human beings will interact with the forest, and what the consequences will be over different time scales.
Further interdisciplinary aspects will examine possible downsides, such as methanogenesis from flooded irrigation schemes and seepage of pollutants into the underlying soil. The study will typically compare the proposed tree-based wastewater treatment to more conventional chemical and physical methods such as coagulation and sand filtration.
Three study sites will be identified in India, one at GBPUAT and two others to be identified with the help of Indian partners. Following assessments of water pollution and health risks, measurements will be made of water influent and outlet qualities with respect to conventional pollutants (e.g. BOD, COD, N, P, K) and of micro-contaminants such as disinfection byproducts and pesticides. Forestry outputs (e.g. calorific value of woody biomass, fodder yield and quality, oil yield) will also be monitored. Dye tracers will be used to study and improve the hydraulic efficiency of the systems. Irrigation and plantation systems will be designed to achieve objectives based on local economic requirements and established water quality criteria.