Table 3: Advantages and disadvantages of UASB reactor technology.

Sr. numberReferences

Advantages of UASB technology

(1)Provides high removal efficiency even at high OLR and low temperature and therefore requires smaller reactor volume[11, 70]

(2) Simple construction and low operation and maintenance cost due to local availability of construction material and other parts[84]

(3) Robustness in treatment efficiency and wide applicability from very small to very large scale[11, 22]

(4)Energy is generated as methane/hydrogen gas. Energy generated can be used to heat the boilers to reduce operation costs. Less energy demand when external temperature control is not required[17, 18]

(5) Less CO2 emissions due to less energy requirement and additional energy production in the form of biogas that can be used to run the system[44]

(6)Low sludge production as compared to aerobic processes. The sludge produced is stabilized having good dewatering characteristics can be stored for extended time periods and reused as an inoculum for seeding UASB reactors[77]

(7)Quick startup time (about one week) by means of granular anaerobic sludge as seed[49]

(8) Ability to withstand organic shock loads[11, 25]

(9)Ability to treat sewage due to availability of macro- and micronutrients and stability of pH without addition of any chemicals[73, 76]

Disadvantages of UASB technology

(10)Needs posttreatment as pathogens are not removed completely, except for helminthes eggs that are successfully entrapped in the sludge. Incomplete removal of nutrients and therefore needing posttreatment[21, 85]

(11)Long startup time is required due to the slow growth rate of microorganisms in case activated sludge is not amply available[20]

(12)Odor, toxicity, and corrosion problem: H2S is generated in anaerobic digestion, particularly when there is high concentration of sulfate in the wastewater. The biogas needs further suitable handling to avoid bad odor. The top gas box and the deflector can be constructed from concrete with epoxy coating to prevent corrosion and gas leakage[85, 93]

(13)In cold regions temperature needs to be maintained within (15–35°C) to achieve steady state performance[5]

(14)A considerable portion of biogas produced may be dissolved in the effluent whose recovery is needed[10, 94]