Sand bioreactors by themselves do not filter out disease causing organisms. Disinfection is needed before surface discharge.
Ultraviolet (UV) light disinfection is an appropriate option for sand bioreactor effluent. When used properly, UV light will destroy bacteria, viruses, algae, and other microorganisms in renovated wastewater. UV light disinfection becomes more efficient as the amount of suspended solids in the effluent decreases. Therefore, sand bioreactors with their extremely clear effluent are especially well suited to UV light disinfection.
When considering UV light, the system design for effluent quality should reflect a worst case scenario. Sand filter effluent typically contains less than 10 mg/l of suspended solids. For design purposes, assume an effluent containing 30 mg/l. In this way, the UV light system should be able to destroy bacteria levels to well below those required for any surface discharge. For recreational use of the receiving stream, fecal coliform bacteria must be within the range of 200 counts per 100 ml to 2,000 per 100 ml on a 30-day average. Fecal coliform limits for irrigation of treated effluent can be as low as 23 counts per 100 ml.
Many other disinfection alternatives are available such as chlorine and ozone, and should also be considered.