Results and discussion
The startup period began on the 19th of October, 2013 where the water temperature in El Berka WWTP water (23–25) °C. A range of (25–30) °C is generally preferred to support more optimum biological reaction rates and to provide more stable treatment [9]. Then the experiment continued in the winter temperature where the temperature ranged between 14 and 16 °C.
Experts suggest that the hydraulic retention times (HRTs) should not be allowed to less than 6 h and it should be less than 18 h during start-up period to treat any type of wastewater. At lower HRT, the possibility of washout is more prominent. This makes it difficult to maintain the effective number of useful microorganisms in the system [10].
During the startup period the wastewater load on El Berka WWTP was high and the COD loading reached about 2000 mg/L, and was reflected on the organic loading fed to the UASB reactor. Then afterward the COD organic loading was in the average range of the treatment plant which ranges between 400 and 600 mg/L. Fig. 3 shows the average influent and effluent COD as well as the COD removal efficiency during the startup period.
The Total alkalinity as calcium carbonate equivalent was also monitored, the alkalinity monitoring importance prevails the assessment of pH, and since the pH values imply the consumption of high amount of alkalinity, reducing the buffering capacity of the medium.
In an anaerobic digester, a bicarbonate alkalinity (as CaCO3) of about 1000–3000 mg/L was required for stable operation [11]. Disparity to this, an average alkalinity with a range of 220–390 mg/L was successful for the operation of a UASB reactor over 200 days [2]. On this basis, sufficient alkalinity was available in the reactor that causes no drop in the pH during the experiment period; Fig. 2 shows the reactor alkalinity during the experiment.