Odor control in sanitation facilities

  • F H Mughal
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Odor control in sanitation facilities

Odor Control in Sanitation Facilities
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Wastewater treatment plants do have the potential to emit odors, in spots or units, where anaerobic system is maintained. In fact, the most pronounced cause of odors in the wastewater treatment plants is the existence of septic (anaerobic) conditions, within the system.

Since, under anaerobic conditions, the microorganisms present in the wastewater have no dissolved oxygen available for respiration, this allows the sulfate-reducing bacteria to thrive. These bacteria utilize the sulfate ion that is naturally abundant in most waters, as an oxygen source for respiration. The result is the production of hydrogen sulfide gas, which has rotten egg-like odor.

Hydrogen sulfide gas has a low solubility in the wastewater, as such, due to its low solubility, it is released in the atmosphere. Hydrogen sulfide gas is also a potential source of corrosion. Other odorous compounds include mercaptans and ammonia.

When I designed the aerated lagoons wastewater treatment plant here in Karachi, in 1982, I was quite particular to ensure that no anxious zones were maintained in the system. In the pump house, in addition to the large-sized windows, I installed huge exhaust fans, to ensure the ventilation rates were good. Ventilation rates for enclosed areas are usually expressed by the number of air changes per hour (ACH), which is calculated as follows:

ACH = Exhaust air flow (cfm) x 60, divided by the enclosed volume (cu ft)

The American regulatory agency (probably, it is Occupational Safety & Health Administration (OSHA), if I’m not mistaken) prescribe ACH rate of 18. I ensured growth of trees on the side, where there was some habitation. I converted all left-over spaces in the plant into the green areas. I never got a complaint for odor from the neighbors.

As against these simple measures adopted by me, it was surprising to read a post in TPO Magazine of 19 March 2015, the odor control measures taken at the James River Treatment Plant in Virginia, USA.

www.tpomag.com/online_exclusives/2015/03...150319_TPO_Sponsored


The staff at the plant found ‘nocardia’ foam from the aeration tanks as the culprit. Decision was made to capture foul air under a cover system so it could be withdrawn and treated in a carbon system.

Various covers were considered. One plan involved covering a portion of the integrated fixed film activated sludge tanks with fixed concrete decks that would serve as both covers and mounting surfaces for the scrubbers. The other portion would be covered with retractable fabric covers that would provide convenient access to the tank internals. Plant workers needed to inspect aeration patterns, clean out anoxic sections and get inside the tanks, when required. These access requirements — along with the possibility of excessive loads that could be imposed on tank walls by concrete lids and scrubbers — led to the decision to design for an alternative scrubber location and cover the tanks entirely with retractable fabric covers instead. – For more details, please see the post.

The bottom line is: while the US is a resourced country, and can adopt costly measures for odor control, simple, cost-effective measures can be adopted for odor pollution control in the sanitation facilities.

F H Mughal

F H Mughal (Mr.)
Karachi, Pakistan
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  • Bhaskar
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Re: Odor Control in Sanitation Facilities

Mr Mughal

Have you considered growing Diatom Algae in the tanks as a solution.

Diatoms consume the nutrients in the sewage and produce oxygen, this prevents anoxic zones and reduces H2S generation.

Diatoms prevent other algae from growing.

Diatoms can be allowed to flow out with the treated sewage and they would benefit the receiving waters, unlike other algae which may harm the receiving waters.

Clean technology promoter.

I am working on a clean technology product to grow Diatom Algae in large waterways. Diatoms account for about 25% of all photosynthesis on Earth and hence are the best solution to consume CO2, N and P and oxygenate water and feed fish.

I am a Chartered Accountant but am now an entrepreneur focussed on clean technology.
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  • kevintayler
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Re: Odor Control in Sanitation Facilities

Thanks to Mughal for the interesting post. I have not much to add on smell problems associated with treatment, apart from to say that anoxic and anaerobic conditions often arise when routine operational tasks, for instance tank desludging, are neglected.

There is another aspect to the issue of smell, the effect on use or otherwise of on-site facilities. There was an interesting paper on this in the April 2013 edition of Waterlines. (See Rheinländer T, Keraita B, Konradsen Fm Samuelson H and Dalsgaard A (2013) Smell: an overlooked factor in sanitation promotion, Waterlines, Vol 32 No. 2, April, pp106 – 112, Practical Action Publishing, Rugby, UK). This gave examples of situations in which people were dissuaded from using on-site facilities, mainly direct-drop pit latrines, by bad smells.

I made notes on this issue and they are imported below:

Surveys conducted in rural Niger and Malawi showed that up to 25% of latrine owners perceived bad smell from human faeces to be a major disadvantage of installing a latrine near the home. (Grimason et al 2000, Diallo et al 2007).

Past and ongoing research in Ghana, a country where 57% of the population used public latrines, has shown that foul smell is perceived to be a major impediment to household latrine adoption (Van Der Geest 2007).

Research among disadvantaged ethnic minorities in Northern Vietnam, children in Scandinavia and schoolchildren in rural Senegal showed that stinking urinals and toilets were perceived as a major barrier preventing children from using school toilets (Lundblad and Hellstrom, 2005, Sidibe and Curtis 2007 and Xuan et al 2012).
Observations in Ghana and Vietnam also show that adults and children prefer alternatives to latrines, including open defecation sites, because of their ‘fresh air’, ‘natural ventilation’ and absence of bad smell (Xuan et al 2012).

The existence of bad smells from latrines is a major barrier to sanitation adoption across continents.


What are the reasons?

‘Although effects of smell have not been quantified and do not correspond with current biomedical germ theories, case studies have shown that latrine users tend to associate smell with health hazards’.

The paper quotes from Mary Douglas and Val Curtis to the effect that people are often more worried about social and aesthetic aspects of unpleasant smells than possible health dangers. The authors state that some users of public latrines in Ghana remove their outer clothes before entering the latrine to avoid smell ‘clinging to their clothes’ after using the facility.

In Vietnam, having one’s own pour-flush latrine was perceived as preventing social conflicts because these latrines could not smell and annoy neighbours (WSP-EAP 2002).
The authors state that the examples show that people feel strongly intimidated by smells from other people or shared latrines, while the smell from one’s own latrine is more socially accepted.
People adopt various strategies to reduce the impact of smells. These include siting pit latrines on the leeward side of households (only possible in fairly low density rural areas). In some places, households use naturally scented substances to neutralise smells. There is an increasing market for synthetic ‘smell chasers’ such as air fresheners and scented cleaning agents.

One technical response has been to provide tight fitting lids to cover the dropping hole, VIPs, which create circulation of air in through the hole and out through a vent pipe and so carry smells away from the interior of the latrine, use of urine diversion toilets, which are said to smell less. Other simple response include adding absorbent materials such as ash, shredded leaves and sawdust, on top of the faeces.

I think that most of these points were based on the paper itself but some may have been based on reading around it. Regardless of this, I agree with the conclusion of the paper's authors that smell is something that needs to be taken more seriously in future sanitation programmes.

Kevin Tayler
Independent water and sanitation consultant
Horsham
UK
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