The attached growth systems have got disadvantages as wel

The most evident advantages of attached-growth biological processes include (Delatolla et al., 2008, 2009; Ramesh et al., 1999):

1. Escalated concentrations of biomass in the reaction tank, which correspond to reduced wastage of biomass.
2. Consortia of aerobic and anoxic metabolic activity in the same biomass ecosystem
3. Lower sensitivity to toxicity effects as well as to other adverse circumstances
4. Up-grading of existing systems at minimum cost
5. Decrease of sludge-settling periods

The attached growth processes require lower energy, they are easy to maintain, have simple operations since operational adjustments are rare, recover favorably well from shock loads and are simple to operate (Metcalf & Eddy, 1991). They are better preferred with regard to “biochemical oxygen demand (BOG) removal, denitrification and nitrification” (Rittman 2006). Attached growth processes make use of the compact nature of technology largely as a result of the possibility of high loading rates that translate into decreased requirements of space during the construction or expansion of facilities on tight sites. The use of fixed biological films to contain microorganisms within the systems brings about stability within the systems. Most of the attached growth processes operate on relatively low energy.

The attached growth systems have got disadvantages as well. They require a large size of land for them to be operative. They function poorly in cold weather and are associated with odor problems. While compared with the suspended growth processes, the attached growth processes do not make proper use of influent carbon for denitrification purposes thus escalated costs due to external sources of carbon. There is minimal operator adjustment in response to changes with regard to loading conditions. These processes require much more capital when compared to suspended growth systems. They also have unfavorable shock load response attributed to fixed quantity of biomass by the biofilm media surface area.