Use of non-parametric methods to investigate the impact of toilet and containment design and operational factors on faecal sludge characteristics at community level: a case study of Mlalakuwa, Dar Es Salaam

Abstract

ABSTRACT Graphical abstract showing the investigation of toilet and containment design and their effects on faecal sludge characteristics in Mlalakuwa Community, Dar es Salaam, Tanzania. The study analysed 37 faecal sludge samples for total solids, total suspended solids, total volatile solids, chemical oxygen demand, pH, temperature and electrical conductivity. Toilet and containment factors included toilet and containment type, containment volume and sludge consistency. Normality assessment, Spearman’s rank correlation and Kruskal–Wallis tests were used to assess relationships. Significant relationships (p < 0.01) were observed between containment volume and total solids, total suspended solids, total volatile solids and chemical oxygen demand; toilet type and total solids, total volatile solids and chemical oxygen demand; and sludge consistency and total solids, total suspended solids and chemical oxygen demand. The graphical abstract concludes that toilet and containment design are key predictors of faecal sludge characteristics. Faecal Sludge (FS) characteristics are critical for effective faecal sludge management (FSM). This study investigated toilet and containment design and operational factors affecting FS characteristics in the Mlalakuwa community, Dar es Salaam. A total of 37 FS samples were collected during discharge at a FS treatment plant and analysed for Total Solids (TS), Total Suspended Solids (TSS), Total Volatile Solids (TVS), Chemical Oxygen Demand (COD), pH, and Electrical Conductivity (EC). Spearman’s Rank-Order correlation and the Kruskal–Wallis test were applied since data were not normally distributed. Containment volume was negatively correlated with TS, TSS, TVS, and COD with ρ = -0.441, ρ = -0.452, ρ = -0.416, and ρ = -0.446, respectively, at p < 0.01, indicating more concentrated sludge in smaller containments. Toilet type showed statistically significant relationships with TS, TVS, and COD with p = 0.005, p = 0.006, and p = 0.008, respectively. Sludge consistency was significantly associated with TS, TSS, and COD with p = 0.002, p = 0.001, and p = 0.001 respectively. Containment type showed highly significant differences in TS, COD, TSS, and TVS (p ≤ 0.002). Containment type and volume, toilet type, and sludge consistency were identified as key predictors of FS characteristics.