1. Check bioreactor for surface ponding. Wastewater should penetrate the sand in a matter of minutes. If wastewater stands on the surface for even a few minutes, begin to take corrective action.
Check the sand used to build the bioreactor. It may be finer than specified or have too high a uniformity coefficient. If this is the case, resting the sand for four months may restore the bioreactor. If the sand is indeed too fine or too nonuniform, continue to use the bioreactor, but at lower application rates. This most likely means the construction of an additional sand bed.
Check the loading rate. Over time, water use may increase or water leaks may develop, causing the loading rate to be more than the designed recommendations. Rest the sand bed for four months and reduce the loading rate. This may mean finding and repairing water leaks or constructing an additional sand bed.
Check the dosing system. Sometimes on/off switches malfunction and the necessary periodic dosing is compromised. A constant, trickle application of wastewater will result in premature clogging. Rest the sand bed for four months and restore the dosing system.
2. Ponding deep in the sand bed can only be observed through an inspection port that extends down to the bottom of the sand. Anaerobic conditions can develop deep in the sand bed causing the formation of a black, mineral crust (iron sulfide) on the sand deep in the bioreactor. Bioreactor effluent will begin to show a brown stain when this occurs. When this begins, corrective action should be taken.
Check the loading rate. Over time, water use may increase or water leaks may develop, causing the loading rate to be more than the designed recommendations. Rest the sand bed for four months or treat the bottom layer of the sand filter with hydrogen peroxide, delivered up through the discharge pipe to oxidize the iron sulfide crust. Most importantly, reduce the loading rate. This may mean finding and repairing water leaks or constructing an additional sand bed.
Check the BOD5 of the wastewater being applied. The sand bioreactors described in this bulletin are intended for domestic sewage following primary treatment. Expected BOD5 levels for this type of wastewater are between 75 and 150 mg/l. If the BOD5 levels are a great deal higher than that, the surface loading rate must be reduced to prevent the creation of anaerobic conditions deep in the sand bed. Rest the sand bed for four months or treat the bottom layer of the sand filter with hydrogen peroxide, delivered up through the discharge pipe to oxidize the iron sulfide crust. Most importantly, reduce the loading rate by constructing an additional sand bed.
3. Check the dosing system. Because they are mechanical systems, pumps with electrical connections should be checked at least once a year.
Conduct a simple pump test to check the performance of the pump, the switches, and the alarm system. If possible, begin by turning off the power to the pump and filling the dosing tank with water up to the emergency level. Turn on the power. The emergency light or alarm should be activated and the pump should come on.
Check the dose volume by filling the dosing tank again with water until the pump turns on and measure the water level in the tank. Continue to pump out water until the pump turns off, and again measure the water level. Compare the drop in inches to the original settings, and based on the inside dimensions of the tank, calculate the dose volume. Use the calculations below for round and rectangular tanks. See calculations below.
For Round Tank
Gallons per inch of depth = tank diameter in
inches * tank diameter in inches / 294
For Rectangular Tank
Gallons per inch of depth = tank width
in inches * tank length in inches / 231
Check the dosing tank for apparent leaks that are bringing excess water into the tank. Look for leaks around the tank inlet and outlet pipes and around the access port.
Visually inspect the wiring for signs of rodent damage, wear, cracks, or corrosion. Do not touch the wiring, because of the great risk of electrical shock. Remember, make no electrical connections inside a pumping chamber because it is a wet, corrosive environment. If damage is evident, rewiring is probably necessary. For more information on proper wiring refer to Ohio State University Extension Bulletin 829, Mound Systems: Pressure Distribution of Wastewater, for sale at county Extension offices.
4. Check the septic tank for necessary pumping. Pumping frequency
can be estimated by:
P = 0.0228 C (V - Qnt)
________
Lned
P = pumping frequency, in years
C = percent solids in septic tank sludge usually 4%)
e = trap efficiency (usually 70%)
d = fraction of solids digested (usually 50%)
n = number of persons served
L = per capita solids loading rate, in pounds per person daily (usually 0.2)
Q = volumetric loading, in gallons per person daily
t = liquid detention time, in days (usually 1 day)
V = tank volume, in gallons
5. Check condition of septic tank inlet and outlet baffles. If a baffle is damaged or missing, replace with a sanitary tee. Also, consider replacing the outlet baffle with an outlet filter to reduce the amount of solids discharged to the bioreactor. (Figure 12, above)
6. Measure wastewater flow to check for leaks and excessive water use. In time, excess wastewater can cause the pump to fail prematurely, or the bioreactor to clog. A simple event counter can check how frequently a pump comes on. Household water meters can be checked for evidence of excess water use.
7. Maintain the sand surface, roof, or earth cover.
8. Watch for changes in surface water drainage. Excess water is the greatest threat to the proper performance of a sand bioreactor. Changes in landscaping near the bioreactors may divert excess drainage water and overwhelm the bioreactor, causing premature clogging. Watch out for surface drainage when new roads or driveways are constructed in the area. Also, divert drainage off nearby building roofs away from the bioreactor.