
v
bacteria inside the laboratory sewer pipe using synthetic sewage. To enhance and promote
film growth, sludge rich in anaerobic bacteria (sulphate-reducing bacteria) was collected from
the anaerobic digester at a local wastewater treatment plant. The second stage of the
experimental program involved monitoring of the laboratory sewer pipe’s aqueous and air
atmosphere inside the pipe. The aqueous phase was monitored for the concentration of
sulphate, sulphide, pH, soluble chemical oxygen demand (COD
s
) and chemical oxygen
demand (COD). The pipe’s atmosphere was monitored for oxygen, H
2
S gas concentrations
and temperature. These parameters were monitored at the inlet and outlet of the laboratory
sewer pipe and the feed tank for different flow rates and sewage characteristics. Synthetic
toilet sewage was used during this stage. A two-phase mathematical model was developed
and used to predict sulphide concentration in sewage and H
2
S concentration in sewer pipe
atmosphere at different flow conditions.
A one-week period of field monitoring was held in two manholes as a part of this project. H
2
S
concentrations were logged by gas detectors inside the manholes. Raw sewage samples were
collected using two auto-samplers and analysed for COD, COD
s
and sulphide. The aim was to
determine the concentration and variation of H
2
S inside the manholes. The results showed that
the levels of H
2
S inside the manholes were around 1 mg/L.
Results showed that using synthetic toilet sewage that contained 29.5 mg/L sulphate, a higher
aqueous sulphide concentration was measured compared to that at 18.2 mg/L. The aqueous
sulphide concentration increased by 89.3% with the 11.3 mg/L increase in the sulphate
concentration. Similarly, a higher COD
s
concentration, 36.8% increase was obtained with a
21.4% increase in the aqueous sulphide concentration. Increasing the sewage velocity by
85.7% increased the sulphide build-up rate by 15.4%.
A model that can predict sulphide concentration in the liquid phase and H
2
S in the air phase in
the sewer at different conditions was developed based on two-phase model using MATLAB
®
software. The model was calibrated using experimental data and used to compare sulphide
concentrations predicted using the model with those obtained experimentally.
The concentrations of sulphide predicted using the two-phase model were in agreement with
those measured using the laboratory sewer pipe in terms of trend but agreement in terms of
value varied. The predictions of H
2
S in the atmosphere were higher by 50 to 85% than