In order to provide a uniform data comparison, a sampling method was developed and applied for selection of 8 samples from different depth levels at the “front” and “back” of the pit for all dry VIPs Figure 1a. Similar approach was followed for the UDDT toilets, where samples were selected from both active and standing vaults Figure 1b. Due to the shallower sludge layers on the School VIPs only four samples were selected from each pit (two from the front and two from the back) and the approach is similar to that of the dry VIPs ( Figure 1c). For the Unimproved pit latrines, an approach illustrated in Figure 1d was followed, as there was no superstructure as for the VIP toilets, hence there were no clear boundaries between the faecal sludge disposed in the pit and the surrounding soil. Wet VIPs were those that had a high liquid content within the pit. Samples were selected from the sludge crust concentrated at the top of the pit and from the liquid beneath the sludge layer but no distinction was made between the front and the back of the pit, Figure 1e. The community ablution blocks VIPs did not allow a structured sampling as with the household dry VIPs and UD toilets.

The selected faecal sludge samples were with capacity of about 1 litre and stored in plastic containers at the laboratory’s cold room at 4°C. Therefore analytical tests were carried out, following standard operational procedures, developed within the Pollution Research Group. Parameters such as totals solids, moisture content, suspended solids, volatile solids, ash content, pH, chemical oxygen demand (COD), nutrient contents, density, heat capacity, thermal conductivity and calorific value were measured.

Total solids were measured following oven drying at 105°C for 24 hours. The following method was used:

Total solids in sample ( mg / 1 ) = ( W 2 − W 1 ) g × 100 000 V sample ( ml ) ( 1 )

W ₂ = weight of residue + filter paper after oven (105°C)

W ₁ = weight of filter paper before oven

V _sample (ml) = Volume of the sample

Moisture content was estimated using the same method as total solids.

MC = m crucible + m faeces − m exit oven m faeces ( 2 )

Where:

MC = Moisture Content

m _crucible = mass of a crucible

m _faeces = mass of faeces

m _{exit oven} = mass of crucible and feaces after drying in the oven

Volatile solids were measured following heating using a furnace at 550°C for 20 minutes. The below equation was used:

VS = m exit oven − m exit furnace m faeces ( 3 )

Where:

VS = Volatile solids

m _faeces = mass of faeces

m _{exit furnace} = mass of faeces and crucible exiting the furnace

m _{exit oven} = mass of faeces and crucible exiting the oven

pH was measured using a pH probe to monitor the degradation of the faecal sludge and the sanitising effects of ammonia. pH also indicates the corrosive effect on pit emptying and sludge treatment devices

COD was analysed using the closed reflux titrimetric method. The COD indicates the degradability rate of the sludge contents.

COD = ( Blank − Titration ) × molarity of FAS × 8000 Sample ( mL ) ( 4 )

COD ( gO 2 / g sample ) = COD ( mg O 2 / L ) Dilution factor × 1000 ( 5 )

Where:

FAS = ferrous ammonium sulphate

mg O ₂/L = milli grams of Oxygen per litre

gO ₂/g sample = grams of oxygen per gram of sample

To measure density,a measure of appropriate volume of 7.5 ml sample is placed oven at 103–105°C overnight.

Db wet ( g / ml ) = W 2 − W 1 V t ( 6 )

Where:

W ₂ – W ₁ = Wet mass of sample

V _t = Total volume of sample (7.5 ml)

Db dry ( g . ml ) = W s V t ( 7 )

W _S = Oven dry mass of the sample

V _t = Total volume of the sample,pore volume + solid volume (7.5 ml).

Ammonia and phosphate content were measures using Spectroquant tests (Merck) for the purpose of nutrient recovery.

Ammonia content as calculated using the following equations:

Wet sample concentration ( g / g ) = A 1000 × V M ( 8 )

Dry sample concentration ( g / g ) = Wet sample conc . ( g / g ) Total solids ( g / g ) ( 9 )

Where:

A = Spectroquant reading concentration

V = Volume of dilution (L)

M = Mass of sludge used in sample preperation (g)

Phosphate content was measured in the following equations:

Wet sample concentration ( g / g ) = A 1000 × V M ( 10 )

Dry sample concentration ( g / g ) = Wet sample conc . ( g / g ) Total solids ( g / g ) ( 11 )

Where:

A = Spectroquant reading concentration

V = Volume of dilution (L)

M = Mass of sludge used in sample preperation (g)

Thermal conductivity, specific heat capacity and calorific value were measured for the purpose of drying, combustion and evaluating the heating potential. The Thermal conductivity was measured by the thermal conductivity analyser from C-Therm TCi. The calorific value was measured using the bomb Parr 6200 Oxygen Bomb Calorimeter.

Sludge volume index (SVI) is an indication of the sludge settle ability in the final clarifier. It is a useful test that indicates changes in the sludge settling characteristics and quality. The SVI was measured by the equation:

SVI ( mg / ml ) = settled sludge volume ( ml / L ) ⋅ 1000 suspended solids ( mg / L ) ( 12 )

Open Science Framework: Mechanical Properties of faecal sludge. https://doi.org/10.17605/OSF.IO/CW5XD [ Velkushanova, 2019].

This project contains data on the total solids, moisture content, volatile solids, pH, chemical oxygen demand, density, nutrient contents and thermal properties of faecal sludge collected in Durban, South Africa, 2012–2014.

Data are available under the terms of the Creative Commons Attribution 4.0 International license (CC-BY 4.0).