The response of nitrous oxide emissions to different operating conditions in activated sludge wastewater treatment plants in Southeastern Brazil.

The continuous measurements of N2O emissions from the aeration tanks of three activated sludge wastewater treatment plants (WWTPs) operated with biological nitrogen removal (BNR) and non-BNR were performed during the different operating conditions of several parameters, such as aeration, dissolved oxygen (DO) profiling and organic shock loading (with landfill leachate). The nitrification process is the main driving force behind N2O emission peaks. There are indications that the variation of the air flow rate influenced N2O emissions; high N2O emissions denote over-aeration conditions or incomplete nitrification, with accumulation of NO2- concentrations. Thus, continuous measurements of N2O emissions can provide information on aeration adequacy and the efficiency of complete nitrification, with major focus on DO control, in order to reduce N2O emissions. An additional concern is the observed propensity of WWTPs in developing countries to receive landfill leachates in their wastewater systems. This practice could have adverse effects on climate change, since wastewater treatment during periods of organic shock loading emitted significantly higher amounts of N2O than without organic shock loading. In short, non-BNR WWTPs are subject to high N2O emissions, in contrast to BNR WWTP with controlled nitrification and denitrification processes.

Parasitological risk assessment from wastewater reuse for disposal in soil in developing countries.

The purpose of this work is to analyze the parasitological risks of treated wastewater reuse from a stabilization pond in the city of Piracicaba, in the State of São Paulo (Brazil), and the level of treatment required to protect public health. Samples were taken from raw and treated wastewater in stabilization ponds and submitted to a parasitological, microbiological and physicochemical analysis. The study revealed on treated wastewater the presence of Ascaris sp. and Entamoeba coli with an average density of 1 cysts L(-1) and 6 eggs L(-1), respectively. For Ascaris, the annual risks of infection due to the accidental ingestion of wastewater irrigation were 7.5 × 10(-2) in 208 days and 8.7 × 10(-2) in 240 days. For Total Coliforms and Escherichia coli in treated wastewater, the average density was 1.0 × 10(5) MPN/100 ml and 2.7 × 10(4) MPN/100 ml respectively, representing 99% and 94% removal efficiency, respectively. For BOD, COD, TS and TSS removal efficiency was 69, 80, 50 and 71%, respectively. The removal efficiency for nitrogen; ammonia nitrogen and total phosphate was 24, 19 and 68%, respectively. The average density of helminths eggs in treated wastewater is higher compared to the density of the limit value of ≤1 egg L(-1) and tolerable risk is above the level recommended by the World Health Organization. Multiple barriers are necessary for the reduction of organic matter, chemical contaminants and parasites from treated wastewater. Standards for the sanitary control of treated wastewater to be reused in agricultural irrigation areas should be compiled for developing countries in order to minimize public health risks.

Water treatment plant sludge discharge to wastewater treatment works: effects on the operation of upflow anaerobic sludge blanket reactor and activated sludge systems.

This experiment examined the effects of the discharge of water treatment plant (WTP) sludge into the following three types of wastewater treatment systems: a pilot-scale upflow anaerobic sludge blanket (UASB) reactor, a pilot-scale activated sludge system, and a full-scale activated sludge sequencing batch reactor (SBR). The UASB reactor received 50 mg of suspended solids (SS) of WTP sludge per liter of wastewater in the first phase, and, in the second phase, it received 75 mg SS/L. The pilot-scale activated sludge system received 25 and 50 mg SS/L in the first and second phases, respectively. The full-scale WWTP (SBR) received approximately 74 mg SS/L. The results of the experiments showed that, despite some negative effects on nitrification, there were positive effects on phosphorus removal, and, furthermore, there was the addition of solids in all systems.

Simultaneous nitrification and denitrification in the activated sludge systems of continuous flow.

This study has investigated the biological nitrogen removal by simultaneous nitrification and denitrification (SND) processes in a system of continuous flow activated sludge (AS) process. The investigation had four stages and evaluated the system behavior under different solid retention times (SRT), food-to-mass (F/M) ratios and dissolved oxygen (DO) concentrations. The data showed that the concentration of DO 0.5±0.2 mgO2/L did not affect the growth of heterotrophic bacteria (2.2-3.1 d-1 at 20°C) and autotrophic nitrifying bacteria (0.16-1.94 d-1 at 20°C), resulting in values very close to those obtained in conventional AS processes. The chemical oxygen demand (COD) removal was over 90% in all stages. The decrease in SRT from 37.2 to 27.8, 19.0 and 10.0 days had no significant influence on the development of SND. In the stage where the carbon/nitrogen (C/N) ratio was 4.3 mgCOD/mgN  L, SND efficiency was of 55%. In the following stages, the C/N ratio was increased and it was possible to achieve efficiencies higher than 98% SND. Overall, the data showed that appropriate controls of carbon and nitrogen input are required to achieve an efficient SND. An established SND technology can save operation time and energy, and might replace the traditional two stages: biological nitrification and denitrification process.