Field-Scale Application of High Rate Anaerobic Reactors for Palm Oil Mill Effluent

Abstract

Palm oil is one of the most rapidly expanding tropical crops in the world. Indonesia and Malaysia are the two largest oil palm producing countries and is rich with numerous endermic, forest-dwelling species. Palm oil milling process generates a large amount of the Palm Oil Mill Effluent (POME). POME is considered the harmful waste for the environment if discharged untreated.

The ponding system is the most common treatment that is employed in palm oil mills to treat POME with more than 85% of the mills having adopted this method. However, the system has a disadvantages that the generated gases are exposed to the atmosphere and it can causes a global warming. On the other hands, closed anaerobic digesting tanks require a short Hydraulic Retention Time (HRT) and able to capture the generated gases.

One of the drawbacks in anaerobic treatment is the difficulty of start up procedures. Major problems of start up procedure are stabilization of microorganism and time-consuming.

Therefore, this study will discuss the performance of field scale closed anaerobic digester for POME treatment during the start up period. In this study, combined system of high rate anaerobic reactors were used for treatment of POME. The reactors consist of Anaerobic Hybrid Reactor (AHR) and Anaerobic Baffled Filter (ABF). The Start up is divided into two part because the first stage was failed. In the first start up, the shock load occurred due to high recycle ratio. During the hydraulic shock load, COD concentration and pH increased rapidly thus first stage was stopped.

The second start up was operated for about 80 days. When the Organic Loading Rate (OLR) increased from 1 to 4 kg/m3/day, COD removal rate constantly maintained above 90%. However, the shock load one more occurred due to high influent COD concentration. Thus, feeding was stopped but circulation was performed during the 2 weeks. After 2 weeks, pH recovered from 5.8 to 6.4 and the result indicates that the activity of methanogen recovered.

On the other hand, accumulation of sludge in the reactor cause the decline of efficiency and clogging. Thus, the accumulated quantity of SS in the primary reactor was calculated. Sludge production per day increased with increasing OLR and maximum sludge production amount was 103 kg/day. It is expected that total sludge accumulated in the primary reactor of 5%. Therefore, it is determined that the primary reactor need to regularly remove the SS in the reactor for stability of the reactor.