In a traditional septic tank system, sludge removal will recover only a small portion of the total nitrogen and phosphorus present in raw domestic wastewater.
The remaining nutrients are therefore being wasted and lost in the ground. Most of the remaining nitrogen and pharmaceuticals pass easily through the soil and can eventually end up in ground and surface waters nearby, causing pollution.
Nitrates and phosphates are used at present by farmers as fertilisers. There is growing concern however that there will be future price increases, because of global shortages of mineral phosphorus. The solution for single homeowners is to recover these nutrients by making home-made compost from human excrement and kitchen waste.
