Speaker: Sarah Tandy Hennessy
Onsite wastewater treatment systems offer cost effective and resource-conserving solutions for populations currently lacking access to safe sanitation globally. Field testing of an onsite blackwater treatment system in India and South Africa demonstrated one onsite treatment system’s feasibility and application in multiple field-testing environments. Stringent disinfection requirements were consistently met at both test sites, in addition to ISO Category B TSS and COD discharge limits. Effluent was clear, colorless and odorless. Further system modifications are required for nutrient removal and more efficient solid-liquid separation. Lessons learned from these field trials are guiding next-generation prototype development.
Introduction:
Thirty two percent of the 4.2 billion people worldwide who lack access to safely managed sanitation reside in India, while 20% live in Sub Saharan Africa (“Home | JMP,” n.d.). Development and innovations supporting the circular sanitation economy are required to treat human waste from these underserved populations. Onsite wastewater treatment and reuse of blackwater provides one strategy for cost-effective and resource-conserving solutions towards this end (Sahondo et al., 2019). The Duke University Center for Water, Sanitation, Hygiene and Infectious Disease (WaSH-AID) developed a treatment system for household-scale use, which treats blackwater onsite to be reused for cistern flush. Identical treatment systems were installed and tested in India and South Africa to test system performance, identify operation and maintenance protocols, and determine design modifications to improve future versions of the prototype (Sahondo et al.; Welling et al.).
Methods:
The systems were installed in female toilet facilities at a private textile mill (India) and a Community Ablution Block (CAB) in an informal settlement (South Africa).
System process flows used and previously described by Rogers et al. (2018) are displayed in Figure 1.1. Solids and liquids were separated in a solid-liquid separator; liquids were treated via a series of settling, active filtration and electrochemical disinfection, while solids were diverted to the sewer. Onsite measurements of turbidity, color, pH, and free and total chlorine were collected regularly. Tests for chemical oxygen demand (COD), ammonia (NH3), total suspended solids (TSS), E. coli, helminths, residual chlorine, total nitrogen, total phosphorus, total coliforms, and faecal coliforms were performed at the lab.
Results and Discussion:
Process Performance: Field testing demonstrated this system was effective at reducing the COD and TSS to levels within ISO Category B (restricted use) standards (Table 1.1). While significant reductions in TN were observed (India: 65% reduction, South Africa 45% reduction) they did not meet Category B discharge requirements. No significant reduction in TP was observed. Turbidity and color were consistently reduced to produce a clear, colorless effluent. Both test sites met stringent disinfection requirements (Figure 1.2).
Influent: One of the largest challenges, and biggest differences, between India and South Africa proved to be the toilet paper in South Africa’s influent which was absent in India’s influent. The solid-liquid separator in South Africa required frequent maintenance, as the toilet paper would jam the mechanical mechanism used for separation. This discovery led to design modifications implemented around the separation mechanism for the subsequent version of the prototype.
Granular Activated Carbon (GAC) 2: Results from both field sites demonstrated while residual chlorine was generated from the electrochemical cell processing, storage of the disinfected waters in the holding tank with the GAC 2 activated depleted the residual chlorine. Future system designs will not include GAC 2 columns based off these field testing results.
System Maintenance: Backwashing of the GAC 1 columns was required at both field testing sites, when the field team observed water backup on top of the GAC 1 columns. GAC replacement was not required at either field test site.
This prototype system performed well during field testing trials in both washing and wiping cultures. Disinfection was consistently achieved, while reducing TSS and COD to ISO Category B standards. Effluent was clear, colorless and odorless. Process design modifications are required to further reduce nitrogen and phosphorous to allowable limits. Design modifications for improving solid-liquid separation for wiping cultures are being explored. Successful testing in both India and South Africa demonstrate this system’s adaptability to multiple testing environments and show its future application for implementation on a wider scale.