**3.10 Comparison of anaerobic reactors**

Anaerobic reactors are comparable by the common features they share, such as HRT, COD removal and OLR (**Table 4**). Supposedly, the best reactor should be able to obtain high OLR, have short HRT and should have high COD removal. Of all the reactors discussed above OLR range from 1 to 30 kg COD/m3 /d. The reactors have an HRT ranging from 1 to 360 hours and COD removal of all anaerobic reactors ranges from 60 to 90%. From **Table 4** the fluidised bed reactor is the best reactor having an OLR of 2 to 50 kg COD m−3 d−1, an HRT of 1 to 4 hours and a COD removal of 80 to 90%. Batch scale anaerobic digestion treating landfill leachate in Nepal (Sisdole landfill) obtained removal of COD as 50% at a retention time of 10 days while it was increased to about 85% using anaerobic sequential batch reactor (SBR) [75]. Due to obstacles in the operation of the fluidised bed reactor, UASB steals the spot of being the best type of reactor with OLR of 2 to 30 kg COD/m3 /d, an HRT of 2 to 72 hours and COD removal of 80 to 95%. This is also after considering issues of convenience in operating these types of reactors. That does not mean other types of reactors are not as good as each situation depends on the type of wastewater and the motivation to treat that specific type of wastewater.


#### **Table 4.**

*Comparison of various anaerobic reactors [53].*
