This article aims to delineate the approach towards the design and operational control of municipal wastewater treatment plants to maintain nitrogen in ammonia-nitrogen form and phosphorus in orthophosphate form in the effluent of the suspended-growth biological systems and, thereby, both of these nutrients in the secondary treatment effluent can be recovered at a subsequent stage in a chemically precipitated form with two-valent cationic ions. Undoubtedly, such biological systems should be designed high-loaded to prevent the development of nitrification, a process which biochemically converts ammonia-nitrogen to mainly nitrate-nitrogen. The chief parameter to control such biological systems towards preventing the nitrification is sludge age. Nevertheless, difficulties towards nitrification control will be encountered in variable flow cases, if flow equalization may not be uniformly applied, which will result in changes at sludge age in the system. Constant sludge age operation under variable flow conditions can be maintained to an extent by maintaining a constant horizontal velocity in the aeration chambers with parabolic cross-section. At high-loaded suspended-growth systems a remarkable portion of organic pollutants is also removed by adsorption on mixed-liquor suspended solids other than bio-oxidation, which contributes to decrease in operational cost due to less need of aeration supply. Additionally, high-loaded systems enhance the specific growth rates of microorganisms, which will give rise to high biochemical substrate conversions at relatively short hydraulic retention times.