Effectiveness of the use of Ag, Cu and PAA to disinfect municipal wastewater.

The WHO defines Category A wastewater as one which does not contain more than 1000 FCU 100 ml(-1) of faecal coliforms (FC) and less than 1 helminth egg (HE) per litre. The objectives of this work were to determine: 1) the disinfectant capacity of different concentrations of silver (Ag), silver-copper (Ag-Cu) and silver-copper-peracetic acid (Ag-Cu-PAA) when added to samples of raw wastewater (RW), with a contact time of 60 minutes; 2) the optimal concentration and contact time required by the better performing disinfectant, determined from the previous stage, to obtain Category A RW; 3) the effect of the selected disinfectant when applied to RW, the effluent of activated sludge (ASE) and the effluent of sand filters (FE) for 10, 30 and 60 min duration. The Ag:Cu:PAA ratio of 0.6:6.0:100.0 mg l(-1), showed the best disinfectant capability to produce Category A wastewater. The ratio of 0.1:1.0:20.0 mg l(-1) of Ag:Cu:PAA and a contact time of 10 minutes are the optimal values to produce Category A wastewater in RW. For RW and ASE, the optimal ratios and times for Ag:Cu:PAA were: 1.2:12.0:90.0 mg l(-1) at 60 min and 0.1:1.0:20.0 for 10 min, respectively. The FE samples showed concentrations of FC and HE below the standards of the WHO; therefore, their disinfection is not necessary.

Adding silver and copper to hydrogen peroxide and peracetic acid in the disinfection of an advanced primary treatment effluent.

This paper evaluates the efficacy of hydrogen peroxide (HP) and peracetic acid (PAA) in the disinfection of an Advanced Primary Treatment (APT) effluent, and how said disinfection capacities can be enhanced by combining the oxidants with copper (Cu2+) and silver (Ag). The treatment sequence consisted of APT (adding chemicals to water to remove suspended solids by coagulation and flocculation), followed by disinfection with various doses of HP, HP+Cu2+, HP+Ag, PAA and PAA+Ag. Microbiological quality was determined by monitoring concentrations of fecal coliforms (FC), pathogenic bacteria (PB) and helminth eggs (HE) throughout the sequence. The results revealed that APT effluent still contains very high levels of bacteria as the treatment only removes 1-2 log of FC and PB, but the reduction in the number of viable helminth eggs was 83%. Subsequent disinfection stages demonstrated that both HP+Cu2+ and HP+Ag have a marked disinfection capacity for bacteria (3.9 and 3.4 log-inactivation, respectively). Peracetic acid on its own was already extremely efficient at disinfecting for bacteria, and the effect was enhanced when combining PAA with silver (PAA+Ag). The best result for HE removal was achieved by combining PAA with silver (PAA+Ag) at doses of 20 + 2.0 mg l(-1), respectively. The study concluded that the PAA+Ag and HP+Ag combinations were good alternatives for APT effluent disinfection, because the disinfected effluents met the standards in NOM-001-SEMARNAT-1996, Mexico's regulation governing the microbiological quality required in treated wastewater destined for unrestricted reuse in agricultural irrigation (< or =1 helminths per litre). Combining either of these disinfection treatments with a primary method such as APT, therefore, offers an effective and practical way of reducing the health risks normally associated with the reuse of wastewaters.

The use of ozone during advanced primary treatment of wastewater for its reuse in agriculture: an approach to enhance coagulation, disinfection and crop productivities.

The purpose of this work was to evaluate the effect that ozone (O(3)) has on the advanced primary treatment (APT) and disinfection of wastewaters for their reuse in agriculture. The enhancement and optimization of APT was done by applying low O(3) doses during coagulation. By applying an ozone dose of 2 mg/L during APT, the required coagulant dose may be reduced by up to 25% to achieve a similar turbidity removal (and up to 50% for total suspended solids removal), when compared to a conventional APT treatment. When the same coagulant dose was applied (60 mg/L), the volume of settleable solids was reduced from 31.0 to 25.5 mL/L, and the settling velocity increased from 0.111 to 0.139 m/min. Disinfection was also improved by the use of ozone, which leads to better plant germination rates than when using chlorination, because of reduced toxicity of the ozonated effluents. Additionally, helminth eggs content was reduced by applying ozone.

Evaluation of phytotoxic elements, trace elements and nutrients in a standardized crop plant, irrigated with raw wastewater treated by APT and ozone.

This project studied the benefits of applying Advanced Primary Treatment (APT) and ozone (O3) to raw wastewater destined for reuse in agriculture. The ozone was applied directly to raw wastewater, as well as to wastewater already treated with APT, and the results compared against a control sample of potable water. The experimental conditions that reported the best results was wastewater treated with O3 (at a dose of 4.8 mg/L, at pH 7, temperature 23 degrees C, for 1 hr), given that it met standards in force in Mexico with regard to micro-organism and heavy metal content. Under these conditions, after 15 min of ozonation, 100% destruction of the following bacteria was observed: V. cholerae, S. typhi as well as total and faecal coliforms. Destruction of helminth eggs and Giardia sp. took one hour. No phytotoxic elements or heavy metals were found. The balance of nutrients N:P:K (300:100:200 mg/kg) required for lettuce growth, was found in wastewater subjected to both treatment plans. However, ozone favoured the nitrification and assimilation of the nutrients, by contributing oxygen to the soil. Therefore, these conditions produced the greatest lettuce growth, the entire plant averaging 38 cm in length and 125 g. in weight. Moreover, a better appearance of the leaves was also noted.

Removal and transformation of recalcitrant organic matter from stabilized saline landfill leachates by coagulation-ozonation coupling processes.

The Bordo Poniente sanitary landfill in Mexico City currently receives 11,500 ton/day of solid wastes. The landfill has been in operation since 1985, in what was formerly Texcoco Lake, now a dried-up lakebed. The physico-chemical characteristics of the leachate generated by this particular landfill are altered by the incorporation of freatic saline water present in the area. This paper reports the results from a study evaluating coagulation and ozonation as alternative processes for removing and transforming recalcitrant organic matter from stabilized saline landfill leachate. Coagulation with ferric sulfate was found to remove up to 67% of COD and 96% of leachate color. The remaining 33% COD was removed with ozone. Recalcitrant organic matter removal by ozonation is limited by the reaction kinetic due mainly to ozone's low reactivity with the organic compounds present in the leachates (amines, amides, alcohols, aliphatic compounds, and carboxylic acids). However, ozone contributes greatly to changing the recalcitrant characteristics of organic matter. Leachate biodegradability was found to be significantly enhanced through ozonation: BOD(5) values reach 265%, and the BOD(5)/COD ratio increases from 0.003 to 0.015. Infrared analysis of ozonated leachates shows that the main by-products of recalcitrant organic matter ozonation are an increase in the hydroxyl and carboxylic groups, and the presence of aldehydes groups.

Characterisation and conditioning of Fenton sludges issued from wastewater treatment.

Characterisation tests were conducted to determine the feasibility of land application of the sludges produced in wastewater treatment by means of Fenton's Reagent. Physicochemical and microbiological parameters of Fenton sludges were compared to the values obtained for raw alum sludges. The Fenton sludges presented preferable characteristics such as the specific resistance to filtration (SRF), metals and pathogen content (fecal and tot al coliforms, helminth ova, and Salmonella sp.). The SRF ofthe Fenton sludges (1.55 x 10(13) m/kg) was 24% less than the alum sludge value (1.92 x 10(13) m/kg). The concentrations of fecal coliforms (0 MPN/g TS), Salmonella sp. (0 MPN/g TS), Helminth ova (22 HH/g TS) and metals correspond to the limits for biosolids of Class B for land application of the Mexican legislation. The Fenton reagent efficiently removes most of the pathogens, considered by the norms, by means of the combined action of the different stages that constitute this process. These results exhibit the Fenton reagent as a feasible treatment for generating sludges with characteristics of biosolids of Class B for land application. The preliminary results of conditioning tests show that Fenton sludges present better dewatering characteristics with regard to the alum sludge, for a dose of cationic polymer of 1 mg/g TS.