Biological processes have been widely employed for wastewater treatment due to their cost-effectiveness and simple design and operation procedures. Attached growth systems, occupying smaller areas and exhibiting lower energy requirements, are suitable for treating sewage of small- to medium-sized communities. A trickling filter is one of the biological-based attached growth systems, consisting of highly permeable packing media in which aerobic condition is maintained via diffusion, forced aeration, natural convection, or splashing. This non-submerged fixed-bed reactor, with or without modifications, has been successfully employed for removing various organic and inorganic matter and pathogens. Adding an anaerobic treatment step before the trickling filter is one of the best modification strategies used to remove high chemical oxygen demand (COD) concentrations. As such, the biological anaerobic process breaks down the complex organic compounds and traps the organic colloids, and then the primary treated wastewater is introduced to the trickling filter process (where the microorganisms grow adhered to a carrier material). This chapter focuses on applying the combined anaerobic-based unit/trickling filter system, as an important strategy for decentralized wastewater treatment. The chapter presents (i) the common treatment systems, such as up-flow anaerobic sludge blanket (UASB) reactor and anaerobic baffled reactor (ABR), used as a pre-treatment stage for trickling filters, (ii) the modifications of trickling filters, e.g., accelo-filter, biofilter, and aero filter, and (iii) the impact of the integrated wastewater treatment systems on human health and environmental sustainability. The outputs of this chapter are suitable for enhancing the wastewater treatment patterns in decentralized communities, which lack complete infrastructure services.