Table 3 Summary of studies assessing sludge accumulation rates, with different variables
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 (1Â 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 | Â | 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. | ||
| Â | Â | 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] | Â | 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 |