Pit Latrine Sludge Research Articles

Attenuation of bacterial hazard indicators in the subsurface of an informal settlement and their application in quantitative microbial risk assessment.

Pit latrines provide essential onsite sanitation services to over a billion people, but there are concerns about their role in infectious disease transmission, and impacts on groundwater resources. We conducted fieldwork in an informal settlement in Dar es Salaam, where cholera is endemic. We combined plate counting with portable MinION sequencing and quantitative polymerase chain reaction (qPCR) methods for characterization of bacteria in pit latrine sludge, leachate, shallow and deep groundwater resources. Pit latrine sludge was characterized by log10 marker gene concentrations per 100mL of 11.2±0.2, 9.9±0.9, 6.0±0.3, and 4.4±0.8, for total bacteria (16S rRNA), E. coli (rodA), human-host-associated Bacteroides (HF183), and Vibrio cholerae (ompW), respectively. The ompW gene observations suggested 5% asymptomatic Vibrio cholerae carriers amongst pit latrine users. Pit leachate percolation through one-meter-thick sand beds attenuated bacterial hazard indicators by 1 to 4 log10 units. But first-order removal rates derived from these data substantially overestimated the longer-range hazard attenuation in the sand aquifers. Cooccurrence of human sewage marker gene HF183 in all shallow groundwater samples testing positive for ompW genes demonstrated the human origin of Vibrio cholerae hazards in the subsurface. All borehole water samples tested negative for ompW and HF183 genes, but 16S rRNA gene sequencing data suggested ingress of faecal pollution into boreholes at the peak of the "long rainy season". Quantitative microbial risk assessment (QMRA) predicted a gastrointestinal disease burden of 0.05 DALY per person per year for the community, well above WHO targets of 10-4-10-6 DALY for disease related to drinking water.

On the compressional rheology of fresh faeces: Evidence for improving community scale sanitation through localised dewatering

Non-sewered sanitation is currently dependant upon pit latrine emptying, the safety of which is compromised by the high costs of faecal sludge transport to centralised treatment facilities. Transport in turn is hindered by the complex rheology of pit latrine sludge. This study therefore characterised the compressional rheology of fresh faeces and modelled the implications for passive (gravity) or mechanical (forced) solid/liquid separation. This informs on the viability of decentralising dewatering for more efficient volume reduction and improving the economics of transportation. The gel point (ϕg) is the solids concentration where the material has a networked structure and signifies the point when mechanical intervention is required for further solid-liquid separation. For fresh faeces, ϕg ranged between 6.3 and 15.6% total solids (TS) concentration. This is significantly higher than the ϕg observed for wastewater sludge at centralised facilities, and it implies that passive gravity driven processes can suffice to improve localised dewatering. The kinetics of passive sedimentation of faecal material were modelled and illustrate thickening from 3 to 10% TS concentration in <0.5 h. This highlights that early intervention to thicken faeces while fresh can improve solid/liquid separation efficiency. Filtration of fresh faeces was characterised by lengthy cake filtration times and comparably short compression times, more similar to mineral slurries than to wastewater sludge. Consequently, fresh faeces presented improved dewatering characteristics, supporting higher final cake solids concentrations and improved dewatering kinetics. By complementing thickening with 300 kPa filtration, a 1.4 cm thick 25% TS product could be achieved in <24 h. Investigation of matrix properties highlighted that increased conductivity (e.g. exposure to urine) negatively influenced dewaterability, an effect which could be mitigated by introducing solid-liquid separation earlier. The thermodynamically favourable compressional rheology of fresh faeces has identified that focussing on localised dewatering could radically improve the economics of faecal sludge management, primarily through reducing transport costs.

Resource-Efficient Characterisation of Pit Latrine Sludge for Use in Agriculture

Resource recovery through reuse of by-products of the sanitation chain presents a great potential towards ensuring universal access to safely managed sanitation. Many developing countries are faced with uncertainty over public and environmental health concerns associated with use of faecal sludge in agriculture. Due to resource constraints, limited data exists on the characteristics of faecal sludge to inform proper and safe use in agriculture. Despite predictive characterisation being demonstrated to be a resource-efficient approach to generate data in other fields, its application in agricultural resource recovery from faecal sludge is lacking in the literature. This paper explored predictive modelling as a less resource-intensive approach for characterisation of nutrients and pathogens in faecal sludge. Specifically, it investigated the extent to which gravimetric parameters could predict nutrients and pathogens in pit latrine sludge from informal settlements in the cities of Malawi. The study explored predictive models to estimate total ammoniacal nitrogen (TAN), total phosphorus (TP), E.coli and helminth eggs from gravimetric parameters (total solids [TS] and total volatile solids [TVS]) in pit latrine sludge. The models developed in the study allow substantially reliable estimation of TAN (R2pred = 75.4%) and TP (R2pred = 78.2%); they also provide moderately reliable predictions for E.coli (R2pred = 69.1%) and helminth eggs (R2pred = 74.3%) from total solids. Since total solids are easy and inexpensive to measure, the models present an option that can reduce resource requirement for characterisation of pit latrine sludge for informed decision-making when using pit latrine sludge in agriculture. In the absence of data on faecal sludge characteristics at the national level, the models provide a starting point for estimation of pathogens and nutrients in sludge for agricultural use. However, stepwise refinement of the models needs to be done through their validation for different types of sludge and inclusion of spatially available demographic, technical and environmental (SPA-DET) data.

Community Faecal Management Strategies and Perceptions on Sludge Use in Agriculture.

Most people in rural areas in South Africa (SA) rely on untreated drinking groundwater sources and pit latrine sanitations. A minimum basic sanitation facility should enable safe and appropriate removal of human waste, and although pit latrines provide this, they are still contamination concerns. Pit latrine sludge in SA is mostly emptied and disposed off-site as waste or buried in-situ. Despite having knowledge of potential sludge benefits, most communities in SA are reluctant to use it. This research captured social perceptions regarding latrine sludge management in Monontsha village in the Free State Province of SA through key informant interviews and questionnaires. A key informant interview and questionnaire was done in Monontsha, SA. Eighty participants, representing 5% of all households, were selected. Water samples from four boreholes and four rivers were analyzed for faecal coliforms and E. coli bacteria. On average, five people in a household were sharing a pit latrine. Eighty-three percent disposed filled pit latrines while 17% resorted to closing the filled latrines. Outbreaks of diarrhoea (69%) and cholera (14%) were common. Sixty percent were willing to use treated faecal sludge in agriculture. The binary logistic regression model indicated that predictor variables significantly (p ˂ 0.05) described water quality, faecal sludge management, sludge application in agriculture and biochar adaption. Most drinking water sources in the study had detections ˂1 CFU/100 mL. It is therefore imperative to use both qualitative surveys and analytical data. Awareness can go a long way to motivate individuals to adopt to a new change.

Application of Process Intensification in the Treatment of Pit Latrine Sludge from Informal Settlements in Blantyre City, Malawi.

Many developing countries lack the infrastructure needed for the treatment of fecal sludge. One limitation in implementing available treatment options is the limited availability of land in the urban areas of these countries. This paper investigated the application of process intensification as a way of reducing the land area required to dewater and sanitize pit latrine sludge from informal settlements in Blantyre City, Malawi. The intensification of the sludge treatment process was achieved by enhancing dewatering through the application of additives and by combining the dewatering and sanitization stages. Nine combinations of sludge, lime and rice husk dosages, in addition to a control, were simultaneously loaded on unplanted drying bed units to dewater for 29 days. The study found a significant reduction of 21% to 73% in the land area required to dewater and sanitize pit latrine sludge. From the study, process intensification was shown to have the potential to significantly reduce the land area required to dewater and sanitize pit latrine sludge from informal settlements in Malawi cities. This makes it an option that can be implemented close to informal settlements, despite land limitation in these areas.

Inactivation of Ascaris for thermal treatment and drying applications in faecal sludge

Abstract Ascaris lumbricoides is the most common helminth of human health importance, and the most resilient helminth found in faecal sludge. There are numerous types of sludge treatments; however, heating and drying are most commonly used for pathogen inactivation. Ascaris suum eggs were heated in a water bath at 40–55 °C for 10 seconds to 60 minutes in water, as well as heated in both urine diversion dry toilet and ventilated improved pit latrine sludge at 40 °C, 60 °C and 80 °C for times ranging from 5 seconds to 120 minutes. Eggs were also spiked into sludges of different moisture contents and incubated over 12 weeks at 25 °C, with samples analysed weekly. Overall, we concluded that eggs were inactivated at temperatures &amp;gt;50 °C, that the temperature–time relationship directly impacted the efficacy of heat treatment, that suspension medium had no effect, and that eggs survived better in wet rather than dry sludges.

Characterization of Faecal Sludge from Pit Latrines to Guide Management Solutions in Cape Coast, Ghana

This study characterised faecal sludge from public ventilated improved pit (VIP) latrines in Cape Coast to assess their potential impact on the environment and to guide the selection of appropriate management solutions. The paper also estimates the amount of beneficial resources wasted due to the lack of a faecal sludge (FS) treatment facility. The study employed a quantitative design involving laboratory analysis of FS sampled from 13 purposively sampled VIP latrines in Cape Coast, Ghana. Sampling activities were carried out in January and February (dry season) and September and October (wet season) of 2015. Samples of unhardened pit latrine sludge were collected from all 13 pit latrines for quality assessment. Physicochemical parameters (moisture content, COD, BOD5, total solids and total volatile solids) of homogenous samples from the surface, middle and bottom of pit contents were analysed following standard procedures. Apart from total solids, all other parameters decreased with the depth of sampling and the differences were statistically significant (p&lt;.01). Seasonal variation in faecal sludge characteristics was not significant except for BOD5. A high COD: BOD5 (3.8-4.5:1) shows faecal sludge that is characterised by slowly degradable organic matter. Even though the FS at the bottom of the pits was found to be the most stabilized, its characteristic parameters indicate that discharging it into the environment without any further treatment would pose a significant threat to public health. The characteristics suggest that co-composting would be the most appropriate option for treating the FS and also underscore the fact that the VIP latrine technology is not suitable for use as a public toilet.

Physico-chemical properties and bacterial community structure dynamics during the mesophilic anaerobic digestion of pit latrine faecal sludge

The study characterized the changes in physico-chemical properties and bacterial community structure during mesophilic anaerobic digestion (AD) of pit latrine sludge. The sludge was sampled from six different pits six times at an interval of 40 days. Standard techniques were used to assess the changes in pollution indicators including COD and faecal coliforms. Metagenomic DNA from a composite sample from the six pits’ sludge was then extracted at Days 0, 14 and 35 and directly sequenced followed by analysis of the microbial structure using the Ribosomal Database Project tools. Multivariate analyses were used to identify the main determinants of microbial community structure during the digestion process. AD significantly reduced the levels of pollution indicators (p &lt; 0.05). Total solids, volatile solids and COD were reduced by 17–27%, 52–79%, and 42– 63%, respectively. The indicator pathogenic microorganisms FC and E. coli were reduced by 34–54% and 35–60%, respectively. The reduction in terms of COD and BOD were, however, not sufficient to satisfy the standards for safe disposal into the environment. Proteobacteria were the most dominant bacterial phylum in the undigested sludge (24.1%) and were significantly reduced to 2.5% at the peak of the AD (Day 14) up until Day 35. Firmicutes significantly increased (p &lt; 0.05) from 22.4% to 28.8% at Day 14 before being reduced to 11.6% at Day 35. This study contributes to our understanding of AD of pit latrine faecal sludge through mesophilic AD as a baseline study, and helps to inform future research on mesophilic AD.

Methods to reliably estimate faecal sludge quantities and qualities for the design of treatment technologies and management solutions

Sanitation access in urban areas of low-income countries is provided through unstandardized onsite technologies containing accumulated faecal sludge. The demand for infrastructure to manage faecal sludge is increasing, however, no reliable method exists to estimate total accumulated quantities and qualities (Q&Q) This proposed approach averages out complexities to estimate conditions at a centralized to semi-centralized scale required for management and treatment technology solutions, as opposed to previous approaches evaluating what happens in individual containments. Empirical data, demographic data, and questionnaires were used in Kampala, Uganda to estimate total faecal sludge accumulation in the city, resulting in 270 L/cap∙year for pit latrines and 280 L/cap∙year for septic tanks. Septic tank sludge was more dilute than pit latrine sludge, however, public toilet was not a distinguishing factor. Non-household sources of sludge represent a significant fraction of the total and have different characteristics than household-level sludge. Income level, water connection, black water only, solid waste, number of users, containment volume, emptying frequency, and truck size were predictors of sludge quality. Empirical relationships such as a COD:TS of 1.09 ± 0.56 could be used for more resource efficient sampling campaigns. Based on this approach, spatially available demographic, technical and environmental (SPA-DET) data and statistical relationships between parameters could be used to predict Q&Q of faecal sludge.

Characterisation of pit latrine sludge from shackleton, a peri-urban residential area of Zimbabwe

Abstract The objective of this study was to characterise the physical and chemical properties of human faecal sludge from various pit latrines in relation to the differences in usage and management practices of each pit over time. Physico-chemical parameters were measured from the sludge collected from the top layers of six different pit latrines that were sampled six times at an interval of 40 days. Data were also collected on pit user habits and management practices. Multivariate statistical analyses were carried out to determine the variations in sludge physico-chemical characteristics among the pits and the associations between these and user habits and management practices. The results showed that the sludge characteristics from the six pits were significantly different from each other (global test sample statistic (R): 0.862 and p &amp;lt; 0.002). This study also indicated that user habits were important determinants of pit sludge characteristics. This study scientifically contributes to knowledge on how pit management and usage practices determine the potential value and quality of pit latrine sludge for various anaerobic digestion applications for resource recovery. The findings also contribute the knowledge required for the management and treatment of pit latrine sludge, adoption and adaptation of new treatment technologies for local use.

Predictive Modelling for Characterisation of Organics in Pit Latrine Sludge in Unplanned Settlements in Cities of Malawi

Predictive Modelling for Characterisation of Organics in Pit Latrine Sludge in Unplanned Settlements in Cities of Malawi

English

Most developing countries use existing knowledge and infrastructure for wastewater in the treatment, reuse and disposal of faecal sludge. There is need to have a clear picture of the risk faecal sludge poses in relation to wastewater if effective treatment, disposal and reuse systems are to be implemented. Little work has been done to quantify the risk faecal sludge poses in relation to wastewater in a localized setting. This study quantifies the comparative risk of faecal sludge from pit latrines in unplanned settlements in Mzuzu City and wastewater. A total 80 sludge samples were obtained from 20 pit latrines in five unplanned settlement Laboratory characterisation was performed for Organics (chemical oxygen demand and biochemical oxygen demand), nutrients (total ammonia nitrogen and total phosphorus) and pathogens (Escherichia coli and helminth eggs) were determined through laboratory analyses. Documentation review was used to get wastewater characteristics. The study found a higher risk (comparative risk &gt;1; p &lt; 0.0001) for organics and nutrients in pit latrine sludge as compared to wastewater. Pit latrine sludge was found not to pose significantly higher public health risk from both E. coli (comparative risk &lt;1; p &lt; 0.0001) and helminth eggs (comparative risk &lt; 1; p &lt; 0.165) than relation to wastewater. Key words: Faecal sludge, environmental risk, public health risk, faecal sludge treatment.

The feasibility of char and bio-oil production from pyrolysis of pit latrine sludge

Energy recovery from bio-oil was feasible when pit latrine sludge with a water content of ≤∼55% was the feedstock.

Occurrence and survival of pathogens at different sludge depths in unlined pit latrines in Kampala slums

Occurrence and survival of pathogens in faecal sludge was investigated in unlined pit latrines at varying depths in peri-urban areas of Kampala city, Uganda. A total of 55 unlined pit latrines, 7 private and 8 rental unlined pit latrines were sampled in the first and second phases (representing the rainy season) and 40 pits in the third phase (representing dry season), and analysed for indicator organisms and pathogens from 4 pit latrine sludge layers, at depths of 0, 0.5, 1.0 and 1.5 m, following APHA standard methods. Physico-chemical parameters of the faecal sludge were also measured. Three sampling phases were undertaken to determine the effect of seasonal variation. Results indicate that the mean temperature and pH were 25.4 ± 1.14°C and 8.0 ± 1.5, respectively; and moisture content increased with pit sludge depth, except between Depths 3 and 4. Average moisture content was 86.3 ± 3%. The measured parameters varied significantly (P > 0.05) between seasons. The mean reduction in total coliforms, thermo-tolerant coliforms, E. coli, and faecal enterococci with sludge depth was significant at all depths (P < 0.05), but the least significant difference was not significant at depth levels of 1.0 m and 1.5 m. Salmonella was only detected at the top layer of faecal sludge in 60% of Phase 2 samples and in only 20% of the samples in Phase 3. About 200–4 100 eggs/g of strongyles were found in 98% of the samples and 100–1 600 eggs/g of ascarids in 55% of the samples. Temperature, pH and moisture content did not show a significant correlation with observed reductions of indicators and pathogens. With extrapolation of the generated regression models, a pit of 8 m can be recommended for reduction of bacteria. It is recommended that protective field gear be used during pit emptying and that faecal sludge treatment should be done to reduce pathogens before disposal into the environment. Keywords : pathogens, indicator organisms, faecal sludge, unlined pit latrine, water contamination

English

On-site sanitation facilities, mostly pit latrines are the main points of human excreta disposal in peri-urban low-income settlements in Kenya. Collection, treatment and final disposal of pit latrine faecal sludge, pose a significant management problem and present public health risks. The choice of appropriate faecal sludge treatment technology depends on precise region based data on the sludge characteristics that are often unavailable. The study analysed physiochemical characteristics of faecal sludge sampled at different depths of pit latrines. Twenty-four samples were collected from six pit latrines along the depth strata at 1-m intervals from the surface to 3 m depth. Samples were analysed for chemical oxygen demand (COD), biochemical oxygen demand (BOD), ammonia, total nitrogen and total phosphorus. The mean COD: BOD ratio was 1:5 with a concentration of 112800 and 24600 mg/L, respectively. Concentrations for all parameters were variable and higher in comparison with properties reported in literature. Upper layers had higher concentrations than lower depths. The concentrations of the sludge were 10-100 higher than acceptable limits for in-fluent sludge into municipal wastewater treatment plants. These results show that disposal of pit latrine faecal sludge into the wastewater treatment plants without co-treatment overload the system since treatment plants in use currently have not been designed to handle pit latrine sludge. The properties of faecal sludge analysed indicate that the wastewater treatment plants may not be capable of treating faecal sludge unless co treatment mechanisms are applied. Therefore, influent faecal sludge must be maintained within allowable concentrations; otherwise, the effluents may lead to significant environmental pollution impacts. Key words: On-site sanitation, depth strata, faecal sludge disposal, low-income settlements.

Retracted Article: The feasibility of char and bio-oil production from pyrolysis of pit latrine sludge

Biochar production is favoured from stabilised pit latrine sludge with lower water and volatile solids content.

Retraction: The feasibility of char and bio-oil production from pyrolysis of pit latrine sludge

Retraction of ‘The feasibility of char and bio-oil production from pyrolysis of pit latrine sludge’ by Tom Bond et al., Environ. Sci.: Water Res. Technol., 2017, DOI: 10.1039/c7ew00132k.

Prevalence and diversity of intestinal helminth eggs in pit latrine sludge of a tropical urban area

The aim of the study was to investigate the prevalence and diversity of helminth eggs in pit latrine sludge in Yaounde, Cameroon. A total of 30 faecal sludge samples were collected in various latrines and analysed for physico-chemical parameters and helminth eggs' characterization was undertaken using standard protocols. Effects of physico-chemical parameters (pH, temperature, salinity, electrical conductivity, chemical oxygen demand, biochemical oxygen demand for 5 days, nitrogen ammonia, dry matter (DM), moisture content) on the parasite eggs were addressed. The total helminth egg concentration in the samples ranged from 8.5 eggs/g DM to a maximum of 264.5 eggs/g DM with a median of 81.1 eggs/g DM. Nematodes represented 67% of the total species followed by Trematodes and Cestodes. The helminth species with high prevalence in the sludge were Ascaris lumbricoides (41.4 eggs/g DM), Ankylostoma duodenale (31.5 eggs/g DM), Fasciola hepatica (34.9 eggs/g DM) and Trichuris trichiura (32.5 eggs/g DM). The physico-chemical parameters had no effect on the parasite concentration. Due to the high helminth egg concentrations in positive samples analysed, the need for proper health and environmental protection measures has to be stressed to prevent helminthic disease transmission due to untreated sludge discharge into the environment after pit latrine emptying or via direct agricultural use.

Lactic Acid Fermentation, Urea and Lime Addition: Promising Faecal Sludge Sanitizing Methods for Emergency Sanitation.

In this research, three faecal sludge sanitizing methods—lactic acid fermentation, urea treatment and lime treatment—were studied for application in emergency situations. These methods were investigated by undertaking small scale field trials with pit latrine sludge in Blantyre, Malawi. Hydrated lime was able to reduce the E. coli count in the sludge to below the detectable limit within 1 h applying a pH > 11 (using a dosage from 7% to 17% w/w, depending faecal sludge alkalinity), urea treatment required about 4 days using 2.5% wet weight urea addition, and lactic acid fermentation needed approximately 1 week after being dosed with 10% wet weight molasses (2 g (glucose/fructose)/kg) and 10% wet weight pre-culture (99.8% pasteurised whole milk and 0.02% fermented milk drink containing Lactobacillus casei Shirota). Based on Malawian prices, the cost of sanitizing 1 m3 of faecal sludge was estimated to be €32 for lactic acid fermentation, €20 for urea treatment and €12 for hydrated lime treatment.

Characterisation and fluidisation of synthetic pit latrine sludge

Half of the world's urban population will live in informal settlements or ‘slums’ by 2030. Affordable urban sanitation presents a unique set of challenges as the lack of space and resources to construct new latrines makes the de-sludging of existing pits necessary, and this is something that is currently done manually, with significant associated health risks. Various mechanised technologies have therefore been developed to facilitate pit emptying, with the majority using a vacuum system to remove material from the top of the pit. However, this results in the gradual accumulation of unpumpable sludge at the bottom of the pit, which eventually fills the latrine and forces it to be abandoned. This study has developed a method for fluidising unpumpable pit latrine sludge, based on laboratory experiments using a harmless synthetic sludge. The implications for sludge treatment and disposal are discussed, and the classification of sludges according to the equipment required to remove them from the latrine is proposed. Finally, further work is suggested, including the ongoing development of a device to physically characterise latrine sludge in-situ within the pit.