K5/2586: Treatment and reuse potential of urine and faecal fractions from urine diversion dehydrating toilets in eThekwini Municipality

Funded by: Water Research Commission

April 2016 to march 2018

Partner Organisations: eThekwini Water and Sanitation; Khanyisa Projects

Project Description:

Over the past decade, eThekwini Municipality in KwaZulu-Natal has installed approximately 90,000 urine diversion dehydrating toilets (UDDTs) at households in peri-urban and rural areas outside the city’s waterborne sanitation zone. EThekwini Water and Sanitation (EWS) recognized that waterborne sewerage systems were not feasible in outlying areas and chose UDDTs as infrastructure that could be managed onsite by household members, thus reducing costs for waste collection and treatment. UDDTs function by separating urine and faeces at the source. At present, the urine is diverted to soak pits, and faeces are collected in a dual vault system for drying following the addition of ash or sand (Roma et al., 2010).

There are two aspects to this project, the first being investigation into the use of black soldier fly larvae (BSFL) to process the sludge, and the second, to investigate the microbial risk of urine-based fertilisers.

Black Soldier Fly Larvae Processing:

While dehydration of faeces in properly functioning UDDTs can reduce the microbial health risk upon contact with material during vault emptying (Gajurel and Wendland, 2004), this risk likely remains important because of the presence and survival of helminth parasites such as Ascaris lumbricoides in the vaults (Trnnberg et al., 2010). The fate of pathogens in faecal sludge in UDDTs in eThekwini has been the focus of several studies (Buckley et al., 2008; Trönnberg et al., 2010).

A common complaint by homeowners served with UDDTs is that they are expected to handle the faecal sludge from full UDDT vaults. Since EWS implemented a free pit latrine emptying service once every 5 years, UDDT users have demanded a similar service for full UDDT and this is to be implemented by EWS. Faecal sludge from UDDTs in the eThekwini municipal region has a high sand content since this is the usual dehydration aid added to the vault by the user after defaecation. The high sand content makes UDDT sludge unsuitable for handling by processes currently used by EWS, including those for pit latrine faecal sludge.

Processing by black soldier fly larvae (BSFL) has been pioneered in South Africa by Stellenbosch University and its affiliates Agriprotein and Biocycle. Black soldier fly larvae have been shown to process fresh faeces and pit latrine sludge (Banks, 2014; Banks et al., 2014), so it can be expected that this would apply to UDDT sludge as well. On this basis, EWS has decided to focus on BSFL as the preferred method for processing UDDT sludge. However, the assumption has yet to be tested fully. Moreover, BSFL are expected to need a readily bioavailable organic substrate in addition to UDDT sludge for rapid growth and organic carbon assimilation. Testing is required to determine which type(s) of additional organic carbon substrate is (are) assimilated best, and which is(are) the most practical to implement at field scale. In addition, the larvae have been shown to be rich in lipid and protein, and BSFL raised on non-faecal organic substrate have been proposed as suitable as feed for fish or other animals.

Use of BSFL as fish food could potentially be used in eThekwini Municipality’s community aquaculture initiative, provided there is no increased health risk to workers or consumers. Similarly, if the residual sludge is shown to pose minimal risk, it could be used as a soil conditioner in small scale agriculture. If the residual sludge is not deemed fit for use, it has been recommended that it be incinerated and used as biochar which also as potential as a soil conditioner, although with a lesser possibility for nutrient recovery. There is therefore more than adequate motivation for investigating the use of BSFL to treat UDDT sludge, and to assess the potential risks and benefits to be gained from utilisation of the larvae and the residual sludge. This study will contribute towards a sound scientific foundation for the development of a business model for UDDT sludge processing, which is funded by the Bill & Melinda Gates Foundation.

Urine-based Fertilisers:

The other fraction produced by UDDTs is source-separated urine. This has been diverted to soakaways in the past, but it is recognised that this process has adverse impacts on the soil surrounding soakaways and also that it represents a neglected resource in terms of plant nutrients. Less attention has been paid to the urine fraction than the faecal sludge fraction since it is typically assumed to be “sterile”, or less contaminated with pathogens than faeces. A number of reports in the literature (Höglund et al., 2002; A Nordin et al.,2009; Nordin et al., 2013), give cause to re-examine this assumption, especially in the light of development and testing of technologies for the recovery of nutrients from urine for use in agriculture in eThekwini (Grau et al., 2012; Etter et al., 2014). While relatively few pathogens are associated with urine itself (WHO, 2006), faecal cross-contamination of urine collected in tanks connected to urine diverting toilets was demonstrated some time ago using faecal sterols (Schönning et al., 2002). Use of faecal sterols to establish the presence of faeces in urine overcomes problems with either rapid die-off (E. coli) or regrowth (faecal enterococci) of faecal indicator organisms in urine (Höglund et al., 1998).

Cross-contamination of urine with faeces introduces a possible pathogen exposure pathway for household members or EWS workers who may come into contact with the urine during handing (Höglund et al., 2002). Several technologies to collect, treat, and reuse stored urine from UDDTs in Durban are under development through the “VUNA” project, a collaborative project between the Swiss Federal Institute of Aquatic Science and Technology (Eawag), the Swiss Federal Institute of Technology in Zurich (ETHZ) and Lausanne (EPFL), the University of KwaZulu Natal and EWS. These technologies include struvite precipitation and nitrification followed by evaporation (Maurer et al., 2006). Field-scale struvite (magnesium ammonium phosphate) reactors have been installed in Durban at the Newlands Mashu research site. Magnesium sulphate is added to to batches of urine, mixing to facilitate struvite crystal formation, and urine is then filtered through cloth bags to capture struvite crystals (Rhoton et al., 2014).

Struvite is subsequently dried at ambient conditions. Laboratory studies have been performed on the fate of a human surrogate phage virus (phi X174) and infective eggs of the helminth parasite Ascaris suum (as a surrogate for the human parasite Ascaris lumbricoides) during struvite recovery and drying (Decrey et al., 2011). Virus was found in similar concentrations in urine and in struvite, but eggs of A.suum concentrated in the struvite cake. Both surrogate virus and surrogate helminth parasite were not fully inactivated during subsequent drying, and the moisture content of the struvite during drying was found to be a key parameter for pathogen inactivation. The transport and inactivation of in situ Ascaris during struvite recovery and drying has yet to be tested a field scale. Preliminary field-scale analysis of bacteria inactivation during pilot scale struvite production in Durban provide indication that current processes would likely be insufficient to fully inactivate Ascaris (Schoger, 2011). A PCR screening study on urine collected in eThekwini showed the presence of a wide range of bacterial and viral pathogens (H. Bischel, unpublished data), lending strong support for further work on the health implications of urine collection, processing and use by EWS (Bischel et al., in preparation). Because pathogens only excreted in faeces were detected in this screening, the study verified that urine collected in Durban is consistently contaminated with faeces. Ascaris was not included in the screening. The detection of high levels of Ascaris in UD vaults in Durban (Trönnberg et al., 2010) and the demonstrated cross-contamination of urine with faecal organisms provide strong motivation for further investigation of the presence of bacterial and viral indicator or index organisms, and Ascaris eggs, in field-collected fresh and stored urine, and in struvite produced from this urine. The die-off of pathogens and pathogen indicators in struvite from field-collected urine also remains to be verified.

Aims:

To better understand the microbial risk associated with the beneficiation of faecal sludge from UDDT toilets using Black Soldier Fly Larvae (BSFL) and Struvite Reactors. The benefits associated with reuse will be balanced against health risks associated with all stages of faecal sludge and urine handling and processing.

Publications and reports

Journal Papers

Posters

Maleba V, Archer C and Rodda N. Treatment of Urine Diversion Sludge using black soldier fly larvae in the context of the legislation and regulations pertaining to management of faecal sludge. Presented at the WISA Conference, Durban, 15th – 17th May 2016