If you want to filtrate green waste water through of sand layer , to be more pure the water, you must use gravey, sand and clay, but finally youmust to do analysis of midrobial testing.
Sand filter is design for removal of Total Suspended Solid and not for removal of BOD/ COD. You have to go for Sewage Treatment Plant. We are consider 135 liter/ Capita/ day sewage generation. The wastewater generation for 200 House Hold calculated as below:
1 House- 5 people
200 House- 1000 people
Sewage Generation: 1000 x 135 liters/1000= 135 KLD
Design Capacity of the STP by considering shock load and Future need is 150 KLD.
There are many types of sewage Treatment Plant. Few are given below:
1. Activated Sludge Process- MBBR or MBR: - Very Compact with clear treated water quality. Treated water can be reuse in garden and flushing. It can be safely discharge in Inland Water body
2. Soil Immobilized Bio-technology (SIBT): required very large footprint area, but almost Zero Operating cost. You Can Develop SIBT as Garden and good looking landscape. Treated water can be safely discharge in inland waterbody.
The problem of a filter whatever it is is to clog up when it is used. As a result it loses immediately and gradually its effectiveness. How to solve this problem? Impossible.
Greywater as all wastewaters contain dissolved pollution. In reality, the reality of all treatment proposals is to reject in the environment, a polluted liquid, making it appear that it has undergone a possible treatment of purification
A filter will retain the suspended material but will not purify the dissolved pollution.
To date all wastewater is discharged into the environment with their dissolved pollution.
With biological sanitation one begins by preserving the characteristic of the water during its consumption, during its use.
Therefore this waste water can be purified by a totally biological device that will reject a clean liquid. This liquid can then be used for the watering of plant biodiversity which it by absorbing the dissolved pollution purifies the soil.
having only Sandfilter as Greywater treatment is not practical at all.
Greywater pollution is mostly made of COD and some TSS. Especially COD will create a lot of MLSS inside of the filter by bacterial growth, leading to frequent clogging of the filter and thus backwash. Furthermore, big material (food rests etc.) will clogg the filter and cannot be treated.
For small communities, better to make some lagoon or similar treatment. Please find some treatment option for decentralised/differenced wastewater treatment in the compendium of EAWAG. It is a real good ressource and best of all, softcopy is for free.
Dear Mary. I cannot give you a detailed answer, but I'm thinking that you could have issues of clogging in your sand filter. If you have enough space, I suggest you to put plants and to build a constructed wetland :). Basically, it's not more complicated than sand filters to manage, and it has shown to be very efficient in treatment of greywater in comparison to other compact technologies, since CW works better for more dilluted greywaters. I suggest you to use gravel, if you have it, and to adopt the horizontal flow scheme, which is the simplest to be managed.
You can find more information on greywater and CWs on the SSWM website (https://www.sswm.info/)
I agree with Anacleto comment above, hence Constructed wetlands might be useful as alternative treatment techniques (low capital and operational costs and do not required qualified persons for operation and maintenance)
Refereeing to your suggestion, as mentioned in some comments above, clogging of the sand filter will be the main problem, and therefore will required periodically backwashing. To minimize the backwashing frequency, I might suggest to fill the column with gravel at the bottom, coarse sand in the middle and fine sand at the top, once the clogging is occurred, you need to replace only the above layer of the fine sand with, in this way you will reduce the frequency of backwashing
I will suggest first, that you need to determine the volume of the generated graywater from the households so may be one of our colleagues in this group can help you by the design of the system.
Finally, I would remind you that if discharge from kitchens will be also included in the system, the household keepers must be aware to remove solids, as possible as they can, before start with washing and don’t discharge oil or fat to the gray water collection system