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Table 3 Summary of studies assessing sludge accumulation rates, with different variables

From: Are pit latrines in urban areas of Sub-Saharan Africa performing? A review of usage, filling, insects and odour nuisances

Source Country Variable of interest Study/experimental design Remarks
DA Still and K Foxon [61] South Africa Number of users Field monitoring and measurements A decrease in per capita filling rate with an increase in number of users.
Rubbish content Sorting and analysis of pit content Throwing rubbish in a pit almost doubled its filling rate
BF Bakare [54] South Africa Number of users Analysis of amalgamated data documented by DA Still and K Foxon [61] No correlation (Pearson correlation coefficient of 0.203) between sludge accumulation rate and number of users.
Field monitoring and measurements Sludge accumulation rates decreased with increasing numbers of users.
Degradation Laboratory experiments on pit latrine samples 50–70 % volume reduction in matter added to the VIP
Addition of moisture laboratory batch experiments on pit latrine samples No evidence that an increase in moisture content of samples from VIP latrines reduced the sludge accumulation rate.
LC Todman, et al. [64] Tanzania Seasonal variation Field monitoring and measurements During wet periods, large temporary increases in the level (1 m magnitude) of pit content was observed
Pit latrine Modelling Modelling pit latrine filling based on model developed by C Brouckaert, et al. [63] Water inflows and accumulation have an important effect on the filling rate
J Norris [59] South Africa Seasonal variation Field monitoring and measurements No effect of season variations on the sludge build up
EG Wagner and JN Lanoix [18] Various Degradation   A possible volume reduction of up to about 80 % after well-established degradation in wet pits
CA Buckley, et al. [62] South Africa Addition of moisture Laboratory experiments on pit latrine samples a significant increase on gas production rate was noted
Increasing Alkalinity Laboratory experiments on pit latrine samples No statistically significant increases in the rate of gas production from the samples under anaerobic conditions.
   additives Laboratory experiments on pit latrine samples Inconclusive results
C Brouckaert, et al. [63] South Africa Pit latrine Modelling Developing and testing a simple mass balance model Adding non-degradable material to the pit significantly influenced its filling
K Foxon, et al. [71] South Africa additives Laboratory experiments on pit latrine samples No statistically significant effect on rate of mass loss
L Taljaard, et al. [69] South Africa Bio additives Laboratory studies on pit latrine samples Use of biological product is feasible
M Jere, et al. [70] Zimbabwe Spore forming bacteria Pit latrine studies Efficient in reducing pit content
FF Kassam [72]   Earthworm (Tiger worms) Laboratory experiment setup Reduction in human excreta
I Banks [74] South Africa Black soldier fly larvae Laboratory studies on pit latrine samples Potential in reduction of pit latrine content