Abstract
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 < 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 < 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.
Highlights
One of the targets of Sustainable Development Goal (SDG) No 6 is for all nations to provide access to adequate and equitable sanitation and hygiene for all, and to end open defecation by 2030 (WHO/UNICEF, 2017)
The aim of this research was to assess the changes in physico-chemical properties and bacterial community structure during the mesophilic anaerobic digestion (AD) of pit latrine faecal sludge, and, secondly, to assess the effectiveness of the digestion to treat the faecal sludge to the quality requirements expected for agricultural re-use and safe environmental disposal, for example, the WHO (2006) guidelines for use in crop production and safe disposal
The study revealed that the process of mesophilic AD of pit latrine sludge reduces pollution indicators in the sludge
Summary
One of the targets of Sustainable Development Goal (SDG) No 6 is for all nations to provide access to adequate and equitable sanitation and hygiene for all, and to end open defecation by 2030 (WHO/UNICEF, 2017). The drive of improving access to clean drinking water and safe sanitation, according to Montgomery and Elimelech (2007), is one of the least expensive and most effective ways to improve public health and save lives. The traditional approach when urban and periurban houses are being built in developing countries is that every community shall be able to have access to sewer-based systems and the ‘flush and forget’ stance shall remain forever. Pit latrines have been constructed in peri-urban settlements of developing countries like Zimbabwe as a faecal sludge management technology to substitute sewer-based systems. Pit latrines are among the affordable on-site sanitation facilities (Torendel et al, 2016) in developing countries, but will eventually fill-up at some stage and must be replaced or emptied. Replacement or emptying causes inconvenience is expensive and a health risk (Torendel et al, 2016)
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