Role of Wastewater Treatment Plants’ Byproducts in Enhancing the Agricultural Sector in Qatar : An Energy, Water and Food Nexus Perspective

The population rise and expected increase of global food demand will put pressure on natural freshwater resources and will result in increased carbon footprint emissions if proper resource planning is not implemented and unconventional water and energy resources are not exploited. The global production of fertilisers, in addition to declining worldwide phosphorus reserves may find it difficult to sustain this rising demand at current capacities. As part of sustainable development, farmers will have to adopt alternative resources that meet the triple bottom line. Wastewater and sludge reuse represent an opportunity for this challenge as they can alleviate the stress on scarce water resources and contribute to the establishment of a circular economy. In addition, treated wastewater contains relatively high amounts of nutrients which can substitute for part of the fertilisation requirements. This project aims to develop a comprehensive and complex framework that allocates the state of Qatar’s generated treated wastewater resources to the different agricultural subsectors. In addition, reclaiming wastewater for the purpose of agricultural irrigation minimizes grey water footprint. The first part of the study suggests an improved grey water footprint model based on two stages.

The first stage consists of a mass balance used to amend the concentrations of the pollutants. As for the second stage, it consists of calculating the GWF based on the Water Quality Index. The second part of the study aims to assess the potential of wastewater and sludge in alleviating the carbon footprint and water stress associated with the agricultural sector and optimize their planning using a multi-objective optimization model and a single objective optimization model under different scenarios. The different scenarios are then assessed using an Energy-Water-Food-Waste nexus approach. A case study was conducted focusing on the agricultural sector in the state of Qatar. The suggested GWF model allows a better breakdown of the GWF required to assimilate the pollution as it outputs 5 different ranges based on the water quality sought as opposed to a single value or range traditionally obtained using existing models.

In addition, the comparison between the improved model and the existing ones demonstrates that the existing models underestimate the GWF if a medium to excellent water quality is to be sought. As for the water allocation, it is demonstrated that the use of treated sewage effluent as a water resource can supply the fodder farms in Qatar with all their N fertilization requirements almost all year long and that the use of both treated sewage effluent and sludge as a source of energy has the potential to reduce the carbon footprint and water stress level by 62% and 57%, respectively. Additionally, a good planning of the water budget can reduce the water stress level to 13.5%.