On-site waste water treatment in Sydingosby

Résumé du document

The project site is a farm located in Sydingösby. The Gunnarsson family is living here. Carina and Stefan have two children. Stefan works at the farm while Carina works at SLU. This site has already a system for waste treatment, but it is not satisfying and not sustainable. Actually it does not permit a good reduction of BOD, nitrogen or phosphorus coming from the waste, and does not offer good recycling of the nutrients. Moreover the family has planned to build a guest apartment, and need to install toilets in the honey room. Thus maybe some of the existing parts of the current one-site system need to be re-dimensioned. And a new system has to be installed to fulfill the aims of BOD, N and P removal. In the first part we are going to describe the site, the current one-site system and the problems which occur. Then we are going to analyze in three other parts three possibilities to improve the waste treatment: the urine diversion, the composting, and the sand filter. We will after that conclude with the system seems to be, according to us, the best choice.

Extraits

[...] The piping system should be as short as possible (10 m long maximum) to limit the time of the urine in the piping system for avoiding precipitation in the pipes and ammonia losses. As other wastewater pipes they should be clearly distinguishable (different colours can be used). A slope of at least should be observed and sharp slope avoided. All the connections should be entirely water tight and connections in the ground should be avoided. The diameter of pipes in the ground is 110 mm. [...]

[...] Urine application can be done during the growing season i.e. from May to the end of September. The application of the urine shall be closed to the ground to avoid aerosol formation and indirectly ammonia losses. Another finding showed that the ammonia losses when spreading the urine were small, usually around and they were never higher than 10% of the nitrogen content. The urine can be used after a short storage time in such situation. Urine cannot be spread on forage according to the Swedish recommendations. [...]

[...] The calculations are presented in annexes. II. Urine diversion system and open sand filter For the first alternative we think about a system with a urine diversion system with flushed faecal material including the installation of a collecting tank for urine then the installation of a fenced open sand filter seems to be a good alternative concerning the purposes of reduction. The current septic tank will be kept. The size of this one is enough to welcome all the wastewater (this decision will be discussed below and calculations are available in appendices). [...]

[...] So this apartment has to be connected to a waste treatment system. The owner said to us that this apartment will be used only 6 month in the year. A planned site for honey handling needs also to be connected to this treatment system, because it will contain toilets according to the law. We also find an old site previously containing liquid manure, an old area close to the farm where nothing may be constructed. Notice that the drinking water comes from a drilled well. [...]

[...] This BOD is associated to the urea concentration. In the collection a big part of the urea is transformed into available nutrients for crops (NH4+). Concerning the emission of gases into the air like NH3 for example, this is avoided because there is no ventilation, the tank will be just pressure equalised. Degradation of urea to ammonia in water in the collection tank: CO(NH2)2 + 3 H2O 2 NH4+ + OH- + HCO3- NH4+ + OH- NH3(aq) + H2O NH3(aq) NH3(g) Concerning the phosphorous, all of is transformed in available nutrient for plants (PO43-, HPO42-, H2PO4-) and precipitation MgNH4PO4 and CaX(OH)y(PO4)Z. [...]