Material Flow Analysis of Phosphorous and Organic Matter in Domestic Wastewater and Food Waste in Sông Công Town, Vietnam

Sammanfattning: Vietnam’s fast economic growth has to a large extent been achieved on the expense of a rapid deterioration of the natural environment, including eutrophication of local water sources. Proper planning is needed to move towards a sustainable wastewater management and one recognized tool for such planning is material flow analysis (MFA). This thesis uses MFA to define the current flows of phosphorus (P) and organic matter, measured as COD, in domestic wastewater and food waste in Sông Công town, Thai Nguyen province, Vietnam. The aim is further to compare two different improved wastewater management scenarios with a business-as-usual scenario. The methods used to find data for the MFA are literature review, interviews and a survey questionnaire. The literature review presents challenges facing the wastewater sector of Vietnam and treatment techniques for wastewater and septage. The wastewater sector is affected by technical difficulties such as lack of capacity and organizational challenges as a result of adjacent and overlapping authorities. Contradictions and gaps in legislation, poor governance, and problems with financing are all issues that need to be addressed. Although the number of wastewater treatment plants in Vietnam is increasing, not more than 10 % of the wastewater is being treated. Various techniques are tried out in Vietnam, among others constructed treatment wetlands and activated sludge techniques, such as Sequencing Batch Reactors and Anaerobic/Anoxic/Oxic processes. These and other techniques are explained and compared in the literature review. From the gathered data three future scenarios for Sông Công’s wastewater and food waste treatment were created along with one of the current situation. The future business-as-usual scenario (BAU-2030) shows the development in Sông Công if no changes are implemented before year 2030, while the centralized scenario (CTP-2030) redirects flows of wastewater to a conventional chemical/biological treatment plant. The third scenario, semi-centralized (STP-2030), implements one treatment plant with enhanced biological phosphate removal (EBPR) followed by a constructed treatment wetland, and a bigger EBPR plant followed by disinfection. Both of the improved scenarios also use food waste and sludge to produce biogas and digestate that can be used as compost in agriculture. The results of the MFA indicate that if nothing is done to change the current management, a 24 % increase of pollutants to the Công River is imminent in just 15 years. On the other hand, if one of the improved scenarios is implemented, 92 % (CTP- 2030) or 90 % (STP-2030) of the P will be available for reuse in agriculture, reducing the need for artificial fertilizer. Further biogas is produced, which can substitute petroleum based gas for domestic purposes or be used to generate electricity.