Increasing the efficiency of anaerobic waste digesters by optimising flow patterns to enhance biogas production

Anaerobic digestion is used to stabilise sewage sludge and produce biogas. Whilst the need to mix digesters is well-recognised, the level of mixing required and its effects on biogas production are not clear. Here, the effects of mixing speed in mechanically-mixed lab-scale digesters on biogas production are considered. For the first time, positron emission particle tracking was used to visualise flow patterns in lab-scale digesters at different mixing speeds. Computational fluid dynamics models were then built to identify the turbulence characteristics. Four lab-scale digesters were run for four months at different mixing speeds and key indicators of digester stability and microbiological population were recorded alongside gas production. Increased mixing speed leads to higher levels of turbulence and in these digesters, increasing the mixing speed reduces the stability of the methane generation process and accordingly has a detrimental effect on the gas production. Similarly, the abundance of methanogenic communities was adversely affected by increasing mixing speeds. However, the unmixed digester produced less biogas than the digester mixed at a low speed, due to uncontrolled digestion. As such, for these digesters, minimal mixing represents the ideal scenario. By considering the velocity gradient in the digester as a surrogate for turbulence, a threshold of 6 8 s-1 was identified. Below this threshold, increased mixing was beneficial but increasing mixing above the threshold was detrimental to digester stability and gas production

Rheology of sludge in pour-flush toilets: understanding the requirements for pit emptying technology design

Pour-flush (PF) toilets are seen as bridging the gap between basic on-site sanitation and the water-borne sewerage systems that people aspire to. Limited studies have been conducted on the rheological properties of PF sludge, which are a key component in designing and selecting appropriate pit emptying equipment. Samples from active and standing PF leach pits were tested for moisture content and viscosity. The two variables were linked using the fresh faeces viscosity model (Woolley et al., 2014). A second model was used to demonstrate how the volume and moisture of material in standing PF leach pits changed over time. This showed that PF leach pits could be emptied using a pump within two months of active use. Alternatively, PF leach pits can be left for up to five years after which the volume will have reduced to 45 % of the original volume and can be dug out manually

Designing pit emptying technologies: combining lessons from the field with systems thinking

The ideal pit emptying machine has been envisioned to be safe, hygienic, and economical, while being mobile and lightweight, allowing access to pits located away from main roads. The machine should be robust, should be amenable to easy operation by a few personnel, and can be maintained using local expertise and supplies. Using the insights from a recent workshop and our own field experience, we discuss the challenges of designing such a machine, and broaden the discussion to include the entire system of pit emptying, collection, and transport. We classify pit emptying technologies according to the type of pit (e.g., wet pits with little trash, wet pits with lots of trash, and dry pits with lots of trash), and argue that designing technologies accordingly should be the focus in the future. A systems approach that includes transport optimisation, sustainability of small businesses, and operator safety and training is advocated

Online course on faecal sludge management: case study in Durban, South Africa

Globally, there is a need for substantially more professionals in the water and sanitation sector. Faecal Sludge Management (FSM) plays a key role for the provision of sustainable non-sewered sanitation and needs to form part of the education of these professionals. In 2016, an online course on FSM was designed and developed by the Global Sanitation Learning Alliance. The course targets professionals working with faecal sludge (FS) systems in developing countries and covers important aspects for the design and operation of comprehensive FSM systems. The first course attracted 80 learners, each of whom paid a fee of $20. Ten learners completed the course. The second course was free and attracted over 350 learners. At the time of writing, the second course is still underway. The course material was updated with links to new technologies and an upgraded online user platform

What happens inside a pour-flush pit? Insights from comprehensive characterization

The pour-flush toilet is extensively used in many countries, but the biodegradation within pour-flush leach pits has not been fully characterised. We present a comprehensive physical, chemical, and microbiological analysis of pour-flush active and standing leach pits in South Africa. Four household toilet sites were sampled four times over 11 months. The pour-flush pit filling rate was estimated to be 0.11m3/y, which is lower than those of other sanitation technologies. Faecal sludge in active leach pits had similar ash, VS, CODT and TKN as other onsite technologies, but higher moisture content. The CODT in pour-flush sludge decreased 85% in 27 days in a short-term laboratory test. Microbial DNA sequencing showed that both aerobic and anaerobic degradation occurred in active and standing pits. Specific microorganisms were identified and differences in microbial communities in active, standing, and single pits were described, providing important insights into processes occurring within pour-flush pits

World Conference on Drowning Prevention 2019, Durban, South Africa

No Abstract

Municipal-academic partnerships for innovation in sanitation delivery: a case study in Durban, South Africa

Service delivery for the diverse communities of eThekwini Municipality requires innovative solutions. The partnership between the Pollution Research Group (PRG) at the University of KwaZulu-Natal (UKZN) and eThekwini Water and Sanitation (EWS) began informally in the 1960s and was first formalised in 2006. The Memorandum of Agreement (MoA) between the two organisations included a retainer that allowed greatly flexibility than would have been possible with project-to-project funding. This allows the PRG to act as an in-house research and development team for EWS and gives the PRG access to numerous research sites. The partnership has led to global recognition for progressive policies and innovative service delivery. It has benefited from interdisciplinary research, trust between organisations and individuals that is built on open and transparent communication, and strong leadership. EWS and the PRG are keen to support similar municipal-academic partnerships across Africa to support locally relevant applied sanitation research

Examining sanitation for urban inclusion, transformation and equity (SUITE) in sub-Saharan African cities

Approximately 70% of the world’s population will be urbanized by 2050. This will increase pressure on already poorly resourced sanitation systems. Solutions must be context appropriate, inclusive and sustainable but can be challenging due to different interpretations of these terms. The aim of the study was to examine current perceptions of inclusion and sustainability of sanitation stakeholders in sub-Saharan African cities in Malawi (Blantyre), Tanzania (Arusha and Dar es Salaam), Zimbabwe (Plumtree), and South Africa (eThekwini Municipality)

Implementing an engineering field testing platform for sustainable non-sewered sanitation prototypes

Researchers globally are developing sanitation solutions that make faecal waste safe, are affordable, do not require external power, water or sewer connections and that recover and reuse water, energy and nutrients. The Engineering Field Testing platform is a collaboration between the Pollution Research Group at the University of KwaZulu-Natal, eThekwini Water and Sanitation and a private company, Khanyisa Projects, which provides a supportive space to test early engineering concepts in a real world environment, while still under the control of technology developers. Local teams of engineers, scientists and social scientists support technology developers through site selection, community engagement, ethical approval, site preparation, installation and commissioning, sampling, testing and feedback and decommissioning. This ensures that locally relevant risks can be identified and mitigated. The concentration of prototypes being tested in a single location allows support resources and expertise to be pooled and increases collaboration to overcome common challenges