Why do public sewers smell so bad

Description:
Objective and reason for the project

Odor emissions from the operation of public sewers pollute residents, passers-by and operating personnel. Furthermore, corrosion processes in the sewers cause considerable economic damage. The aim of the project was therefore to test possibilities that prevent or reduce the formation of hydrogen sulfide and the resulting corrosion. Originally, the focus when working on the project was on the use of biofilters. However, the problem of odor and corrosion is so complex that there cannot be an ideal or universal solution. Therefore - depending on the initial situation - different variants were examined. First of all, a new filter technology for sewer systems, such as breathable adsorbers in the shafts, was developed and tested. Additives for wastewater in the sewer system, such as iron hydroxide sludge as waste products from drinking water treatment, were also successfully tested. Furthermore, possibilities for structural changes and for the operational management of the wastewater drainage systems were examined.


Presentation of the work steps and the methods used In order to develop new filter technology, after a pre-selection of the material, mainly pelleted iron hydroxide sludge (EHS) from drinking water treatment was tested in various series of tests. The focus of the investigations was on the reduction of H2S emissions and the resulting filter resistance as well as the lowest possible obstruction to air access into the shaft
1. Dosing of waste products from drinking water treatment
In practical trials lasting several weeks, the dosage of untreated iron hydroxide sludge (EHS) and pellets in sewers contaminated with H2S was investigated. Stoichiometric basic values ​​were determined by determining the waste water quantities, the hydrogen sulphide loads in the sewers, the dosing quantities of the EHS and its concentration. Other chemicals were also used for comparison.
2. Structural changes
First ideas for structural changes to existing systems were z. B. tested by constructive changes to the ventilation of manholes in laboratory tests.
3. Development of solutions
In order to simplify the complex problem recording and the development of solutions for the operator, a first draft for computer-aided data recording and evaluation was developed to accompany all experiments.


Results and discussion

The use of pelletized iron hydroxide sludge as filter material has led to good results in the tests carried out.
On the one hand, this filter material is significantly more breathable than the previously used biofilter materials and thus does not lead to a further increase in the aggressiveness of the canal atmosphere to the same extent.
On the other hand, the test results to date indicate a service life of more than a year, which, however, must be determined more precisely in the practical test that is currently still running.
Taking into account the low production costs, a more economical alternative to the previous products should be available.

The tests with the direct dosing of iron hydroxide sludge from drinking water treatment in H2S-contaminated channels have confirmed the already known positive effect. By determining stoichiometric basic values, attempts were also made to install a controlled, wastewater-dependent dosage. With a favorable local location, the filter flushing waste water from drinking water treatment in regions with ferrous groundwater can be discharged directly into the sewers and dosed in an economically sensible way. Alternatively, the addition of pelleted iron hydroxide sludge was investigated in comparison to commercially available chemicals and it was found that in many cases this can be more cost-effective with the same effect.
In addition, through the investigation of problem areas in sewage disposal systems, it was found that poorly functioning ventilation systems and incorrectly dimensioned pressure lines exacerbate the problems of odor and corrosion. First ideas for eliminating these deficiencies - such as B. the construction of other ventilation devices for manholes - have been successfully tested in laboratory tests, but require further investigations for practical usability. This also applies to inliners of variable diameter for pressure lines or pipe coatings that prevent drainage.
An important finding is the fact that only location-dependent complex solutions can be promising in the long term and that a detailed, technically well-founded preliminary investigation is therefore required in each problem area, as a result of which the various solution modules can be proposed.


Public relations and presentation

4 Water symposium Odor and Corrosion in Drainage Networks of the Lausitz University of Applied Sciences in April 2002 with conference proceedings
4 Interim report of May 20, 2003 was distributed to all special-purpose associations involved
4 The final report is also distributed to the special-purpose associations involved
4 articles in the trade press are planned.

The project also includes:
4 the brochure of the Water Symposium Odor and Corrosion in Drainage Networks of the Civil Engineering course of the Lausitz University of Applied Sciences (Volume 9/2002),
4 the interim report of RSC Rohrbau und Sanierung GmbH dated June 2nd, 2003 and
4 the detailed final report of April 8, 2004.


Conclusion

In the project, a functionally better and more economical alternative to the currently available biofilters for sewage shafts was successfully developed.
In addition, there are other approaches, some of which have already been tried and tested in practice, to avoid / reduce the corrosive load on sewer systems and the odor of their surroundings.
Provided that the useful life of the new filter material in the large-scale test corresponds to the laboratory test carried out, it can be assumed that a cost saving of 30 to 40% can be achieved compared to the filters currently on the market. When using iron hydroxide sludge products for direct dosing in sewage systems, cost savings of more than 50% are achieved compared to commercially available products