Treatment of olive mill wastewater using an anaerobic sequencing batch reactor

Wastewater from olive mills in Jordan has been characterized and treated using a lab scale anaerobic sequencing batch reactor (ASBR). It was found that this wastewater has an average COD:N:P ratio of about 900:5:1.7. At this ratio, the wastewater was found to have sufficient nutrients that it was not necessary to add nutrients or combine it with other wastewaters. For effective treatment it was necessary to reduce the strength of the wastewater with an average COD value of about 97 g/L, to about 16 g/L by keeping part of the treated wastewater in the reactor when a new batch of wastewater was added. This achieved more than 80% COD removal at 3 d hydraulic retention time and at an organic load of about 5.3 kg COD/m3/d provided that alkalinity was added to adjust the pH to near 7. The specific substrate utilization rate, and observed biomass yield were about 0.37 kg COD removed/kg VSS/d, and 0.06 kg VSS/kg of COD degraded, respectively.

The following conclusions can be drawn from the present study: • Removal efficiencies of COD, phenol, FOG, and TSS using ASBR with 3 d retention time and at an organic load of 5.3 kg COD /m3/day was equal to 83, 63, 99, and 91%, respectively. • OMW in Jordan has sufficient nitrogen and phosphorous concentrations that addition of such nutrients was not necessary, nor was it necessary to combine it with other wastewaters. • The COD:N:P ratio required for anaerobic treatment of wastewater should be calculated from a formula that takes into account the removal efficiency and observed yield for the wastewater in concern (45.5/EYobs:5:1) instead of using a constant value for all • different wastewaters, or based on loading rate. Dilution of the OMW was necessary for the anaerobic treatment of such wastewater. This was achieved by adding raw OMW to the reactor containing treated OMW from the previous batch. This, in addition to no nutrient requirement, substantially reduces the cost of treatment.