Stricter regulations in the field of sanitation are driving new dimensions of analysis, in which socioeconomic criteria combined with associated environmental issues are in turn increasing the complexity of wastewater management. In this environment, the development of innovative wastewater treatment technologies provides decision-makers with many efficient alternatives to face these new challenges. This growing number of alternatives inevitably leads, however, to ever greater complexity in the design or upgrade of treatment facilities and demands the acquisition and integration of updated knowledge and well-co-ordinated expertise, encouraging a multi-disciplinary approach. In this paper, it was demonstrated that these requirements have been successfully met in a environmental decision support systems (EDSS). The EDSS was built according to a knowledge-based methodology, whose main objective is the identification and assessment of the most appropriate wastewater treatment technologies for the design of new facilities or the upgrading of obsolete plants. Because removal of nutrients is essential to this approach, this study explores the use of the EDSS to address the selection of biological treatment technologies for different scenarios characterized by wastewater composition (C/N ratio) and other relevant criteria such as environmental and economic factors, population size, discharge in sensitive areas, reuse, cost-benefit analysis, life-cycle analysis, and technical aspects (use of innovative technologies, space availability, reliability, and simplicity of operation).

The concept of one-stage reactor system for biological nitrogen removal over nitrite of ammonium high loaded sidestreams is going to be applied to remove nitrogen from anaerobically digested sewage sludge and to achieve its complete stabilisation. Dealing with sludge, the organic matter needed to denitrify is present in the inflow as particulate substrate, which requires a hydrolysis step. The latter implies high anoxic hydraulic retention time (HRT). During both aerobic and anoxic phases, ammonium is released which implies the need to enlarge aerobic HRT. Both effects lead to a total HRT higher than those for nitrification-denitrification of wastewater with soluble substrate. The purpose of this paper is to define, by computer simulation, a set of theoretical criteria, which will be applied later to the operation of a pilot-scale post-aeration reactor to be located in a Spanish WWTP. These criteria will be defined by simulating the reactor performance under different operating conditions. As a conclusion, some operation guidelines have been established for the above-mentioned scenario in terms of aerobic and anoxic retention time, dissolved oxygen concentration and effluent requirements (NH4 (+), NO2 (-) and NO3 (-)).

The paper presents a systematic study of simulations, using a previously calibrated Colloid model, from which it was found that: (i) for pure moving-bed biofilm reactor (MBBR) processes with tertiary nitrification conditions (no influent chemical oxygen demand (COD)), dissolved oxygen = 5 mg/L and residual NH4-N > 4 mgN/L, a nitrification rate of 1.2 gN/(m(2)d) was obtained at 10 W C. This rate decreases sharply when residual NH4-N is lower than 2 mgN/L, (ii) for MBBR systems with predenitrification-nitrification zones and COD in the influent (soluble and particulate), the nitrification rate (0.6 gN/(m(2)d)) is half of that in tertiary nitrification due to the effect of influent colloidal X-S (particulate slowly biodegradable COD) and (iii) for integrated fixed-film activated sludge (IFAS) processes the nitrification rate in the biofilm (0.72 gN/(m(2)d)) is 20% higher than for the pure MBBR due to the lower effect of influent X-S since it is adsorbed onto flocs. However, it is still 40% lower than the tertiary nitrification rate. In the IFAS, the fraction of the nitrification rate in suspension ranges from 10 to 70% when the aerobic solids retention time varies from 1.4 to 6 days.