Coliform bacteria removal from sewage in constructed wetlands planted with Mentha aquatica.

The present study evaluated the performance of the species Mentha aquatica in constructed wetlands of horizontal subsurface flow (CW-HSSF) with regard to the removal of coliforms bacteria in an effluent from the primary treatment of sewage as well as to obtain adjustment parameters of the bacterial decay kinetic model along the length of the CW-HSSF. Therefore, four CW-HSSFs measuring 24.0 m x 1.0 m x 0.35 m were built and filled with number 0 gravel as the support medium to a height of 0.20m. Two of the CW-HSSFs were planted with the species M. aquatica, while the other two remained uncultivated. Cultivation of M. aquatica in CW-HSSF resulted in total coliforms (TC) and Escherichia coli (EC) removals from 0.9 to 1.3 log units greater than those obtained in the uncultivated experimental plots, for the hydraulic retention times (HRTs) of 4.5 and 6.0 days. For HRT ranged from 1.5 to 6.0 days, the highest removal efficiencies in counts of TC and EC were obtained when using longer HRT. The mathematical models evaluated showed good fit to average counts of TC and EC highlighting the modified first-order kinetic model with the inclusion of the power parameter in the HRT variable.

Treatment of wastewater from coffee bean processing in anaerobic fixed bed reactors with different support materials: performance and kinetic modeling.

An evaluation was performed of three upflow anaerobic fixed bed reactors for the treatment of wastewater from coffee bean processing (WCP). The supports used were: blast furnace cinders, polyurethane foam and crushed stone with porosities of 53, 95 and 48%, respectively. The testing of these 139.5 L reactors consisted of increasing the COD of the influent (978; 2401 and 4545 mg L(-1)), while maintaining the retention time of 1.3 days. For the maximum COD applied, the reactor filled with foam presented removals of 80% (non-filtered samples) and 83% (filtered samples). The greater performance of the reactor filled with foam is attributed to its porosity, which promoted greater collection of biomass. From the results, it could be concluded that the reactors presented satisfactory performance, especially when using the foam as a support. Furthermore, the modified Stover-Kincannon and second order for multicomponent substrate degradation models were successfully used to develop a model of the experimental data.

Influence of organic loading on an anaerobic sequencing biofilm batch reactor (ASBBR) as a function of cycle period and wastewater concentration.

The effect of organic loading on the performance of a mechanically stirred anaerobic sequencing biofilm batch reactor (ASBBR) has been investigated, by varying influent concentration and cycle period. For microbial immobilization 1-cm polyurethane foam cubes were used. An agitation rate of 500 rpm and temperature of 30+/-2 degrees C were employed. Organic loading rates (OLR) of 1.5-6.0gCODl(-1)d(-1) were applied to the 6.3-l reactor treating 2.0 l synthetic wastewater in 8 and 12-h batches and at concentrations of 500-2000mgCODl(-1), making it possible to analyze the effect of these two operation variables for the same organic loading range. Microbial immobilization on inert support maintained approximately 60 gTVS in the reactor. Filtered sample organic COD removal efficiencies ranged from 73 to 88% for organic loading up to 5.4gCODl(-1)d(-1). For higher organic loading (influent concentration of 2000mgCODl(-1) and 8-h cycle) the system presented total volatile acids accumulation, which reduced organics removal efficiency down to 55%. In this way, ASBBR with immobilized biomass was shown to be efficient for organic removal at organic loading rates of up to 5.4gCODl(-1)d(-1) and to be more stable to organic loading variations for 12-h cycles. This reactor might be an alternative to intermittent systems as it possesses greater operational flexibility. It might also be an alternative to batch systems suspended with microorganisms since it eliminates both the uncertainties regarding granulation and the time necessary for biomass sedimentation, hence reducing the total cycle period.