No abstract

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 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.

The following study was carried out as part of the environmental monitoring of a landfill in Nuevo Laredo, Tamaulipas (Mexico). The parameter of field capacity is important in predicting the amount of leachate generated by solid waste disposal sites, because of the polluting potential of leachate. This paper describes how the field capacity for municipal solid waste was determined, and the purpose of this document is to present a methodology, and to describe the devices designed for determining the field capacity of municipal solid waste. The method consists of applying a surcharge to a representative sample of rubbish, to simulate the effects of the overlying layers in a landfill. The experimental results showed that the higher the compaction of the sample, the smaller the amount of water required to satisfy the field capacity and thus to start the leaching process. Standardisation of the methodology for determining this parameter is required in order to be able to compare the results with those obtained in other parts of the world.

Helicobacter pylori is a pathogen bacteria associated with chronic gastritis, peptic ulceration, and gastric carcinoma. H. pylori has a spiral morphology, which under certain conditions of stress becomes a coccoid form. This type of morphology has been linked to a viable but non-culturable (VBNC) state, which is thought to allow its persistence in the environment. Membrane damage in VBNC H. pylori in water as a mechanism for inactivation using ozone (O) and chlorine disinfection has not been reported in the literature. In this paper, disinfection assays with ozone and chlorine were conducted to evaluate their effects on VBNC H. pylori cells. The use of fluorescent dyes such as propidium monoazide (PMA) coupled with quantitative real-time polymerase chain reactions produced results necessary to assess the viability of the microorganism and demonstrate the effect of each disinfectant on the bacterial count. Applying ozone showed a 5-log bacterial reduction using a disinfectant concentration and exposure time (CT) of 4 mg min/L. Chlorine disinfection for the same 5-log reduction required a higher CT value. Field emission scanning electron microscope images of ozone-treated VBNC H. pylori also showed severe cell damage. The use of PMA revealed that chlorine produced physical damage in the membrane in addition to the known inhibiting effect on cell enzymatic processes. These findings are important for the detection and control of VBNC H. pylori cells in drinking water systems.