Citizen science to enhance evaluation of local wastewater treatment - a case study from Oslo.

The paper discusses how citizen science within an ecosystem services (ESS) framework may enhance evaluation of de-centralized water solutions. In a demonstration case in Oslo, citizens were engaged in long-term monitoring and evaluation of two solutions for treatment of combined sewer overflows. The citizens participated in the design of the study, systematic observations, and final evaluation, via interviews and workshops. A wealth of real-time information was collected, supplementing simulation data and water sampling results. The concept of ESS drew attention to benefits that tend to be ignored in standard evaluations. It is, however, most elaborate for ecological services, and less developed for social aspects. Involving the citizens complemented the framework in these areas, while providing new insights into the contextual interactions influencing ESS and benefits of local treatment. Both solutions, a cross-flow lamella settler and a high-rate filtration system, were quite efficient in removing suspended solids, with a strong impact on visual appearance. A range of wider benefits were identified. These were difficult to monetize, but the citizens' evaluation provided an alternative measure. The study highlights the benefits of citizen science in local water management and suggests the need for more research on beneficiaries in ESS evaluation.

High rate filtration for local treatment of combined sewer overflow.

Combined sewer overflows (CSOs) pollute receiving waters and have a negative impact on ecosystem services. In urban areas rehabilitation of the sewer system to avoid CSOs is associated with high investment costs. Furthermore, not all CSOs can be closed due to the need for hydraulic reliability of the system. Local treatment of CSO with high rate filtration offers an alternative to rehabilitation of the sewer system that is flexible with respect to design and has lower investment cost than separating sewage and storm water runoff. Results from DESSIN, a 4-year EU demonstration project, are presented. The results showed on average 50% removal of particulate matter during CSO events, with higher removal (80%) in the initial first flush period. Other constituents, for example heavy metals, were removed through their association with particles. Potential impacts on ecosystem services in the catchment and the sustainability of the solution were assessed.

Study of an organoclay for the sorption of dissolved organic compounds in the wastewaters from offshore platform operation.

The goal of this research work was to find a sorbent able to selectively retain the harmful dissolved compounds in the wastewaters from offshore platform operation but not the carboxylic acids and to study the effects of the most important parameters on the sorption process. BTX compounds (benzene, toluene and p-xylene) and acetic acid were chosen as the representatives of the harmful compounds and carboxylic acids groups respectively since they are found in the highest concentrations. An organically modified clay was determined to be the most suitable sorbent, where performance was evaluated at different values of pH (3, 5 and 8), acetic acid concentration (0, 160 and 320 mg/l), salinity (0, 35 and 70 g/l) and temperature (20, 40 and 60 degrees C). Results show that there is a sorption competition between BTX and acetic acid. Sorption of BTX compounds decreased with increasing initial acetic acid concentration and temperature, and increased proportionally with the salinity. Sorption of acetic acid, however, decreased with increasing pH, temperature and salinity.

Effect of organic loading rate on a wastewater treatment process combining moving bed biofilm and membrane reactors.

The effect of moving bed biofilm reactor (MBBR) loading rate on membrane fouling rate was studied in two parallel units combining MBBR and membrane reactor. Hollow fiber membranes with molecular weight cut-off of 30 kD were used. The HRTs of the MBBRs varied from 45 min to 4 h and the COD loading rates ranged from 4.1 to 26.6 g COD m(-2) d(-1). The trans-membrane pressure (TMP) was very sensitive to fluxes for the used membranes and the experiments were carried out at relatively low fluxes (3.3-5.6 l m(-2) h(-1)). Beside the test with the highest flux, there were no consistent differences in fouling rate between the low- and high-rate reactors. Also, the removal efficiencies were quite similar in both systems. The average COD removal efficiencies in the total process were 87% at 3-4 h HRT and 83% at 0.75-1 h HRT. At high loading rates, there was a shift in particle size distribution towards smaller particles in the MBBR effluents. However, 79-81% of the COD was in particles that were separated by membranes, explaining the relatively small differences in the removal efficiencies at different loading rates. The COD fractionation also indicated that the choice of membrane pore size within the range of 30 kD to 0.1 microm has very small effect on the COD removal in the MBBR/membrane process, especially with low-rate MBBRs.

High-rate wastewater treatment combining a moving bed biofilm reactor and enhanced particle separation.

Many cities around the world are looking for compact wastewater treatment alternatives since space for treatment plants is becoming scarce. In this paper development of a new compact, high-rate treatment concept with results from experiments in lab-scale and pilot-scale are presented. The idea behind the treatment concept is that coagulation/floc separation may be used to separate suspended and colloidal matter (resulting in > 70% organic matter removal in normal wastewater) while a high-rate biofilm process (based on Moving Bed biofilm reactors) may be used for removing low molecular weight, easily biodegradable, soluble organic matter. By using flotation for floc/biomass separation, the total residence time for a plant according to this concept will normally be < 1 hour. A cationic polymer combined with iron is used as coagulant at low dosages (i.e. 1-2 mg polymer/l, 5-10 mg Fe/l) resulting in low sludge production (compared to conventional chemical treatment) and sufficient P-removal.

Biological phosphorus and nitrogen removal in a sequencing batch moving bed biofilm reactor.

Biological phosphorus and nitrogen removal in biofilm processes have a potential advantage compared to activated sludge processes, because of less vulnerability with respect to sludge loss and because biofilm processes, in general, are more compact with a smaller footprint. Experiments have been carried out in a moving bed biofilm reactor operated as a sequencing batch reactor (SBR), with simultaneous nitrification, phosphorus uptake and denitrification in the aerobic phase. In order to achieve good phosphorus and nitrogen removal, the length of the anaerobic period should be tuned to achieve near complete removal of easily biodegradable COD in the anaerobic period, and the length of the aerobic period should be long enough for complete nitrification. The total COD-loading rate must be at the same time be kept high enough to achieve a net growth of biomass in the reactor.