Wastewater treatment using fibrist and saprist peat: a comparative study

Geochemical characterization and biomonitoring of reclaimed soils in the Po River Delta (Northern Italy): implications for the agricultural activities

This geochemical study is focused on the easternmost part of the Po River alluvial plain in Northern Italy, which is interested by widespread agricultural activities, investigating a reclaimed sector of the Province of Ferrara, known as "Valle del Mezzano" (Mezzano Low Land, hereafter reported as MLL) characterized by peat-rich soils. The chemical-mineralogical characterization of these reclaimed soils is important to compare the local geochemical backgrounds with those recorded in other sectors of the River Po plain and to monitor if the observed concentration exceeds critical thresholds. The reported analyses include (a) measurement of the soil salinity, (b) nutrient evaluation, (c) major and trace element concentrations carried out on bulk soils, (d) tests of metal extraction with both aqua regia and EDTA to highlight the distinct elemental mobility and (e) phyto-toxicological measurement of heavy metal concentrations in plants (Lactuca sativa acephala) grown on the studied soils. The results indicate (1) high soil salinity, often with drastic increase of sodium and chloride along the soil profiles, (2) high nitrogen content (in part related to anthropogenic activities) on superficial horizons and nitrate decrease along the soil profiles and (3) comparative enrichments in heavy metals with respect to other soils of the province, which indicate that peat deposits are effective in trapping metals from anthropogenic sources. This, in turn, implies potential geochemical risks for the agricultural activities. In this regard, specific concerns are related to the high nickel and arsenic content of MLL soils due to the mobility of these elements and their attitude to be taken up by plants.

Removal of particles in organic filters in experimental treatment systems for domestic wastewater and black water

This study assesses the total suspended solids (TSS) retention capacity of different organic filter media for two potential applications: (i) a polishing unit for package treatment plants and (ii) a pretreatment for blackwater from low-flushing toilets. The results showed that the peat filter media used can be significantly improved in terms of structural stability and TSS removal capacity by mixing it with sawdust. Most of the TSS accumulated in the upper part of the filter material, and filter thickness exceeding 15 cm had no statistically significant effect (P < 0.1) on the TSS treatment performance. The experimental system reached a TSS reduction of 60-70% for blackwater and 80-90% for simulated effluent peaks from a package treatment plant. The main challenge of a full-scale application of an organic filter is the issue of clogging, especially when treating concentrated blackwater. However, this work indicates that a clogged filter media can be regenerated by mixing the uppermost filter layer without significant loss of filter performance regarding TSS. More research is needed to develop an appropriate mechanical unit for automatic filter media regeneration.

Dual-stage peat beds in small community wastewater treatment

In this study, the quality of water treated by two dual-stage peat bed systems was compared with a single-stage system, and a costs analysis was performed. The experiment was carried out on a pilot scale using pre-treated urban wastewater. The pilot setup consisted of a single-stage system with a hydraulic loading of 0.6 m(3)/m(2)d, and two dual-stage systems. The first of these worked with hydraulic loadings of 1.2 and 0.6 m(3)/m(2)d for the initial and second stages respectively. For the second dual-stage system hydraulic loadings were 1.8 and 0.9 m(3)/m(2)d. In comparison with the single-stage system, the dual-stage systems produced effluents with a substantial improvement in physicochemical quality (suspended solids, COD and BOD) and microbiological quality (faecal and total coliforms). Quality parameters were similar to a conventional system, meeting the legislative standards of European Union Directive 271/91 for wastewater treatment. Total costs of the peat-bed systems showed a reciprocal X-model regression depending on the average daily volume of urban wastewater to be treated, with a tendency towards convergence of costs between the single and dual-stage systems. The main problem with the dual-stage systems is the greater surface area required for their installation, which can be estimated by linear regression depending on the average volume of water to be treated per day.

Evaluation of municipal wastewater treatment plants with different technologies at Las Rozas, Madrid (Spain)

Eight small-scale municipal wastewater treatment plants were evaluated over a period of 19 months in the suburb of Las Rozas in Madrid (Spain). Four plants used compact extended aeration, two used conventional activated sludge, two used conventional extended aeration, one used a rotary biodisc reactor and the other used a peat bed reactor. The best results were obtained from the plants that used conventional technologies and the biodisc. Conventional activated sludge and extended aeration had higher removal efficiencies for ammonia, TSS, COD and BOD(5) and produced good quality final effluents for final disposal in accordance with the discharge standard. Empirical equations that correlated the concentration of dissolved oxygen in the effluents with the efficiencies of TSS, ammonia, COD and BOD(5) removals for all plants evaluated were obtained. The performance of the plants using compact extended aeration was affected more than those using conventional technologies or rotary biodisc when the capacity exceeded that of its initial design.