There are quite few separate processes which go together to provide a SAFE AND RELIABLE source of non-potable rain harvested and recycled water supply.
Activated Sludge tertiary treatment is a very effective way to treat grey water, solids waste filtrate and other input streams described above. The image below shows the 5x200L polythene drums which have been modified to suit the Activated Sludge process requirements.
It is a biological process requiring a relatively small input of energy (ie: pumping and oxygenation) and is relatively low maintenance if the system is well designed. Treatment relies on an adequate detention time where input effluent streams are exposed to biological processes.
After Tertiary treatment the liquor is passed through a Secondary Treatment comprising a Constructed Reed Bed and a Gravel bio-filter to allow further biological processes. The below image shows the end of the reeds and the start of the gravel bio-filter.
More settling of solids continues in the shallow channel where the treated water is exposed to natural UV. Water then passes into the pond where 75% of the surface is covered in floating rafts which house more reeds and other aquatic plants with roots trailing into the water.
Slow Sand Filtration
As treated water accumulates in the buffer storage in the pond and the treated water storage tanks a decision is made to allow the water to circulate further OR transfer to the main storage tank. All water in the treated water tanks has been passed through the Slow Sand Filter. Slow sand filters work through the formation of a gelatinous layer (or biofilm) called the hypogeal layer or Schmutzdecke in the top few millimetres of the fine sand layer see here. The water produced from an exemplary slow sand filter is of excellent quality with 90-99% bacterial cell count reduction.
After passing through the slow sand filter I pass the filtrate through UV Treatment at a maximum rate of approx. 100L/hour.
This limits the flow rate through the Slow Sand Filter which ensures uniform, safe water quality.