It takes from four to eight weeks to start up a new sand bioreactor to produce a high quality effluent. Naturally occurring microorganisms in the wastewater, sand, and even air, begin to colonize the surface of the sand grains with the first application of wastewater. As wastewater application continues, the microorganisms grow and form a biofilm on the sand grain surfaces. The effluent quality reflects the biofilm formation. Over the first few days of wastewater application, the effluent may appear cloudy from any fine clay and silt particles washing out of the sand. From then on, sand bioreactor effluent is extremely clear.
CBOD5 levels and ammonia levels drop steadily after the first few days of wastewater application. When ambient temperatures are near 70oF, nitrification begins within the first two weeks of wastewater application, and full nitrification is observed within one month. At cooler ambient temperatures, the same pattern occurs, but will take longer to fully develop.
To minimize start-up time and potential environmental impact, new bioreactors should be established during warm weather. Once established, sand bioreactors are extremely resilient to fluctuations in loading. During periods of low or no loading, the microorganisms utilize food and nutrients stored in the biofilm itself. Short term high loadings can stress the biofilm by decreasing the amount of air that flows through a more flooded bed of sand. Because the microbial film is fixed, it does not wash away and is ready to continue renovating wastewater.
The primary goal of sand bioreactor management is to manage clogging. Sand bioreactors are predisposed to clog over time. This is an important fail-safe feature of sand bioreactors that acts to protect the receiving environment from poorly treated wastewater. The predisposition to clogging also penalizes the negligent treatment system owner.
Unlike mechanical treatment plants that require extensive training and daily attention, sand bioreactors are extremely easy to manage, requiring little time or training. Unfortunately, maintenance free systems do not exist, so no one has the luxury of totally neglecting their wastewater treatment system.