DATA-DRYING-ISOTHERM-FAECAL-SLUDGES.xlsx

Sample Collection

On-site
sanitary wastes were received from the Pollution Research Group, at the University
of KwaZulu-Natal, South Africa. The sludges were collected from the following
sources: a) anaerobic baffled reactor (ABR) at a decentralized wastewater
treatment system (DEWATS); b) VIP latrines and c) urine-diverting dry toilet (UDDT).
The DEWATS is a mixture of black water, greywater and human faecal sludges and
it receives effluent from neighbouring households and communal ablution blocks in
Fraser's informal settlement, Durban. Due to the limited size of the inlet of
the DEWATS, samples were collected during pit emptying and using a vacuum truck.
For representative sampling of the DEWAT, samples were collected from 3 zones (top,
middle and bottom) of the settling tank (first compartment). The VIP samples
were collected directly from a vacuum truck, following the emptying of a VIP pit
in Bester informal settlement, located 25 km north of Durban. The FS sample
from the UDDT was collected from Kwamashu, 20 km north of Durban, a facility that
serves a single household. FS samples from the UDDT were collected manually
from the top, middle and bottom using spades and forks. Large household waste
(clothing, sanitary material, paper, etc.) found in the sludge were removed
onsite. For consistent and representative sampling, bulk samples have been
collected from multiple points, screened for materials larger than 5mm (using a
sieve) and mixed to a uniform consistency. The samples were kept at 4ºC
and couriered to Cranfield University in plastic bottles under the
authorization of the Health Department of the Republic of South Africa, through
the export permit with the reference J1/2/4/2. The collection and analysis of FS
for this investigation were approved by the Biomedical Research Ethical
Committee from the University of KwaZulu-Natal (Ethical Clearance Reference:
EXM005/18).

After collection, the faecal sludge samples
were stored in a cold room at 4°C at the laboratory of the Pollution Research
Group. The faecal sludge was shipped inside tightly sealed containers to avoid
moisture loss. At Cranfield University, fresh human faeces (HF) was collected
from a volunteer in a cardboard bowl with the sample contained in a plastic bag
and container as approved by the Cranfield Research Ethics Committee Approval
(CURES/2310/2017). Samples were stored at 4°C and brought to room temperature before
analysis. To determine the initial moisture content of the samples, 5 g of the
samples was weighed and dried at 105 ± 5°C in a hot air oven. Table 1
highlights the initial moisture content of the samples as received from the University
of KwaZulu-Natal and Cranfield.

Thermogravimetric
analysis

Under
isothermal drying conditions, 40 mg of sample was thinly spread in a cylindrical
aluminium crucible to a diameter of ~3 mm and weighed to an accuracy of ± 0.5
mg. Samples were subjected to controlled temperatures of 55, 105, 85, 155, 205°C
in a thermogravimetric analyser (Model: PerkinElmer
TGA 8000™). All experiments were carried out using an airflow rate of 40
mL/min. Prior to isothermal temperature, samples were raised from 30°C to the specified
temperature at a rapid heating rate of 100oC/min to minimise drying
during the heating-up stage. Average results for triplicate analyses are presented for four (4) samples: ABR, HF, UDDT, VIP for 5 temperatures (55-205oC).