3.19 Reuse of wastewater for irrigation of a snail farm

Technical Description

The Mantar Kft. edible snail processing factory was established in Nyiregyhaza, Hungary, in 1993. Processing consumed 110 m³/day of drinking water during the processing season which lasts for four months. The amount of resulting wastewater is about 60 m³/day. Originally, the treatment of this wastewater was difficult because of the high chemical oxygen demand of the water (almost 3 000 mg/l) and the high concentration of sodium salts added as cleaning and whitening agents during the washing of the snail shells. While the amount of sodium salts Used in this process could be reduced to about 60 kg/day, no other chemicals suitable for cleaning and whitening the shells of the snails were readily available. Mechanical and chemical pre-treatment of the sewage with ferric chlorite and lime cream, however, was able to reduce the COD by up to 70%. Notwithstanding, final disposal of the treated wastewater was problematical due to the lack of a suitable receiving surface waterbody.

In order to obviate the problem of sewage disposal, the factory decided to establish a snail stock-farm, where the treated sewage could be reused as the water supply to irrigate the feeding plants. To retain the irrigated effluent within the snail biotope, a ridged poplar tree filtering system has been planted, and fencing installed on the ridges to prevent the migration of the snails and any direct contact with the polluted water. Until the cultivated snail's breeding plants reach an optimum size, the farm is irrigated with clean water to maintain a moist environment.

Extent of Use

This technology is known to be used at only one site in Hungary.

Operation and Maintenance

The operation and maintenance of this technology includes repairs and control similar to that traditionally used in snail farming and processing schemes.

Level of Involvement

This technology is implemented at the company level.

Costs

The capital cost of investment in the treatment facility and additional improvements was $76 800. The cost of the snail breeding farm and required equipment is estimated to be $48 000.

Effectiveness of the Technology

This technology is fully effective in utilizing food processing wastewater from an existing factory for production purposes.

Suitability

This reuse technology is suitable for use in similar situations where food processing factories backward integrate into food stuff production, and where favourable climatic conditions exist (e.g., light winters).

Advantages

The utilization of the mechanically and chemically- pretreated sewage is very economical, and serves as a means of conserving the irrigation water supply.

Disadvantages

No disadvantages have been identified.

Cultural Acceptability

This technology is an accepted and efficient wastewater treatment technology.

Further Development of the Technology

The technology is complete in itself.

Information Sources

PetKovac and Dr Korna H. Kocsis, FelsTisza - Vid Kezetvlmi Fels 4400 Nyiregyh, Szenyi u.19, Hungary, Tel. (36-42) 310 155, fax: (36-42) 310 713.