In line with a R187 million expansion project to improve the ageing infrastructure in Buffalo City Municipality, the Reeston Wastewater Treatment Works in East London has undergone an upgrade to increase its capacity to 12.5 Mℓ/day.

As part of the Reeston Wastewater Treatment Works (WWTW), QFS was responsible for the fast delivery and implementation of an I-BOx® 7010 odour control unit.

The odour control was installed for the inlet works section of the plant, as these areas are highly prone to hydrogen sulfide (H₂S) generation due to the turbulence created through degritters, screens and various other equipment. The turbulent water allows the gases contained within the water to be released as the water follows its course though the inlet works.

The H₂S released in these works can be a severe safety concern for the roughly 80 personnel operating at the Reeston WWTW, with high concentrations leading to severe safety risks of operators, as per Table 1.

 

H2S concentration	Toxicity	Effect
0.1 – 3 ppm	Odour threshold
3 – 10 ppm	Offensive odour	Rotten egg smell
10 – 50 ppm	Headache, nausea, throat and eye irritation
50 – 100 ppm	Eye injury	Leads to serious eye injury
100 – 300 ppm	Conjunctivitis, respiratory tract irritation, olfactory paralysis	Coughing, eye irritation, loss of smell after two to five minutes
300 – 500 ppm	Pulmonary edema	Imminent life threat
500 – 1 000 ppm	Strong nervous system stimulation apnea	Loss of consciousness, death possible in 30 to 60 minutes
1 000 – 2 000 ppm	Death	Rapid unconsciousness

Table 1 Toxicity and effects of H₂S at various concentrations (Source: ‘Odor prevention and control in process plants’, Chemical Engineering, Feb 2002, pp. 50 – 55)

 

The importance of odour control

Table 1 categorically highlights the importance of odour control and its effect on plant safety for operators. Typically, H₂S concentrations measured at inlet works are around 300 ppm, which can cause severe discomfort and necessitate additional medical care and treatment for personnel affected.

This could lead to minimised personnel on-site, which would mean fewer operators to maintain and operate equipment, which can ultimately lead to strain on the plant and therefore strain on metropolitans and communities, as sewage cannot be treated effectively.

By implementing odour control measures such as the I-BOx, these safety concerns can be effectively mitigated, ultimately improving worker safety and the functioning of wastewater treatment plants.

 

Article by Annejan Visser, process engineer at QFS