Micro sewage solutions
While planning our outdoor kitchen, shower and toilets we had to figure out a solution for the waste water. Because the planned area was about 200m away from our reed-bed system, that was installed last year, i researched about some smaller decentralized solutions. Which could be built up easy, cost extensive while still delivering a proper treated waste water.
I came across one of the best resources on the web that is covering like every aspect of sanitation there is:
under this link you can find a lot of studies, ideas and examples what is possible today in terms of alternative sewage solutions:
http://www.susana.org/en/resources/akvo-sanitation-portal#akvopedia:Sanitation%20Portal
Kitchen Grey Water Solution
Greywater: is a wastewater fraction which is not heavily polluted. It includes wastewater from hand wash basins, showers, kitchen sinks and household appliances like washing machines or dishwashers and excludes toilet wastewater. The major pollutants are thus derived from soaps, shampoos, detergents, sweat, dead skin, hairs, oil and grease. The contamination by pathogens in grey-water is considered to be very low due to the absence of toilet wastewater.
So fore our own purposes i came up with an under sink solution for the grey water that is produced by the kitchen sink. This grey water has one big problem which is the high amount of grease and fat that is produced while cooking. As a hot substance grease is fairly fluid and runs free with but water and oil do not mix. As the grease cools it clogs due to the fact it is not soluble in water. This fats will lead to clogging in the tubes and will create problems in the sand filter.
So i came across professional grease traps that are used in the food industry. They function basically with a chamber system which allows the oils to raise to the surface while the sludge sinks to the ground.
As shown in the picture above the water enters at the first chamber on the left side and runs passively through the next chambers in to the last one on the right side. Because the particles we want to separate will float to the surface our connections between the chambers have to be at the bottom. The first chamber has a slightly risen connection because there will still be some slurry, like small pieces of food, that need sink down (sedimentation). In order to reduce the particles i have seen some nice ideas that make use of a bucket filled with straw that sits over the first chamber. The straw acts as a filter mesh for bigger parts and can be, when filled, easily emptied on a normal compost heap.
While taking care of the grease we and up with normal grey water that is depending on the soap used no big deal for a well designed and maintained sand filter. The Sand Filter can be easily connected with an over flow pipe after the Grey water chamber. In the sand bed a drainage pipe distributes the overflow evenly with in the vertical filter bed.
The Filtered Water tank can be used to keep fish. You can use them as bio indicator to check on the filtration quality of the System (if bad, fish goes dead). How ever keep in mind that in most European states it is not allowed to use processed grey water for irrigation on edible plants. The picture beneath shows the over all setup of the system.
Sizing of the Sand Filter
As general rule, the required area is 1.25 m² of filter surface per 100 L of grey-water a day. To ensure proper functioning of the filter the surface should be at least 1 m² and should have a minimum depth of 70 cm for horizontal flow and 100cm for vertical flow systems. The sand filter can be planted to avoid clogging. The main treatment process encompasses the retention of particles by the filter material and cleaning processes due to biological activity in the biofilm on the sand. So the plants are good but not needed for the processing of the water.
Specific water consumption by different household appliances, per person (Friedler 2004).
Hand wash basin 15 L / person / day
Bathtub 20 L / person / day
Shower 20 L / person / day
Kitchen sink 25 L / person / day
Dishwasher 5 L / person / day
Washing machine 20 L / person / day
Design alteration
The same system could be build with a variety of materials and ready available containers or scrub material like old bathtubs. A widely available cheap container is the blue plastic barrel so here is the system again in blue:
Resources used:
GREYWATER TREATMENT IN SAND AND GRAVEL FILTERS
Low Tech Solution for Sustainable Wastewater Management
Manual for Design, Construction, Operation and Maintenance
Author: Lukas Huhn, June 2015
Technology review of constructed wetlands
Subsurface flow constructed wetlands for greywater and
domestic wastewater treatment
Authors: Dr. Heike Hoffmann, Dr.-Ing. Christoph Platzer,
Dr.-Ing. Martina Winker, Dr. Elisabeth von Muench, Eschborn, February 2011
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