Hydrogen Sulfide Reduction In Waste Water Collection Systems

By Harriett Crosby


Hydrogen sulfide is a colorless gas produced when organic matter is being broken down by bacteria in absence of oxygen. This procedure is usually referred to as anaerobic digestion and can occur in swamps and sewers. It can also occur naturally as natural gas or in volcanic gases. This gas has a characteristic smell of rotten eggs no wonder the foul smell usually produced by sewers. It is no wonder specialists are concerned with hydrogen sulfide reduction in the sewer system.

With the production of the gas in sewer lines, environmental specialists usually worry about the odor and corrosion troubles. People who live near sewer lines often complain of the odor issue while the municipal usually worries about infrastructure destruction through corrosion. This usually results when water in the system mixes with the gas forming hydro sulfuric acid that corrodes the surfaces.

There is thus need to control the production of this gas in waste water collection system to very low levels. One way which specialists have found to reduce production of this gas is through addition of a strong alkali or soluble basic solution. The basic solution for instance sodium hydroxide (NAOH) or magnesium hydroxide when added to sewage increases the pH and this leads to limited formation of the gas.

The other method is chemical treatment where certain chemicals are released into the sewer. More often than not, chloride compounds are the ones usually fed into the system. Examples of these compounds include; calcium and sodium hypochlorite, ferric chloride or bleach. When any of these compounds are added to sewage, they lead to oxidation of sulfides hence the gas will not be formed.

However this addition of chemical compounds can be challenging when there is no pumping post from which the chemicals are fed into the system. Therefore a chemical feed system should be established to make this process easier. The feed system should also be monitored to ensure effective treatment system. Safety measures are usually considered when carrying out this chemical treatment.

When it comes to corrosion problems there are certain measures that are taken to reduce or prevent this. Increasing ventilation in the sewer infrastructure to prevent break down of organic matter conditions with no oxygen is one way. The other way is through the use of protective coatings on tanks and sewer pipes on their inner part. These coatings are usually composed of tar products, polythene linings, vinyl, cement, plastics and many other materials.

The other method of corrosion control is crown and manhole spraying. Usually, corrosion is worst at the crown of the pipe since the acid collects at this point. This causes the pipe to weaken and eventually collapse if the problem is persistent. Spraying a Sulfa Lock Hi Gel onto the manhole and sewer surfaces protects them from harsh effects of the acid.

Lastly, a monitoring instrument called the liquid phase sulfide meter has been formulated to help in observing sulfides levels in industrial wastes. If the instrument shows the sulfide to be higher than the wanted amount, the waste undergoes pre treatment before its release to the waste water collection system. All in all, these strategies on hydrogen sulfide reduction have helped a lot in control of the negative effects of the gas. But specialists are still coming up with other methods to manage this issue more effectively.




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