Articles

The primary and biological sludges from municipal wastewater treatment plants represent its main solid residue. Because of its high organic load and the content in nitrogen and phosphorus compounds, the sludge may be used in agriculture. In order to check the possibilities to use for application in agricultural lands, the anaerobic fermented sludge was characterised for the following physicochemical and bacteriological parameters: total N, P, heavy metals, fecal coliform. The analyses were conducted in compliance with the Romanian standard methods as follows: total N content varies between 36.7-44.6 g/kg d.s., from which NH4+–N represents ≤ 10%, and NO3––N does not exceed 0.9%; P expressed as P2O5 is 1.2-2 g/kg d.s., and K evaluated as oxide (K2O) presents values of 3-5 g/kg d.s; the analysed heavy metals have lower concentration values than the limits for a biological sludge used as a fertiliser in agriculture, in conformity with Directive 86/278 EEC; according to EPA, the municipal wastewater treatment plant residual sludge, treated by anaerobic fermentation, is included in B class sludge. Pathogens indicators analysed for this class of sludge are – the density of fecal coliform, indicator which can be analysed in the same manner as Escherichia coli, the most important pathogen agent from this category of microorganisms. According to the norms of EPA, a sludge which is going to be used as an agricultural fertiliser must contain a smaller number than 2 millions colonies formatting units (CFU) per gram of total solids in the moment of its use. The results were compared with the Norms stipulated by Decree 49/14 January/2004 for approval of the Technical norms concerning the protection of the environment and especially for the soil when the sludges are used in agriculture. The results show that the sludges from the Romanian Municipal WWTPs may be used as fertiliser for less sensitive culture like: textile plants and pasture field.

Sludge reuse is one of the main challenges of waste management and an action with environmentally consequences that must be kept under control. The progress of civilization leaded to the globally increase of sludge production. WWTPs treatment technologies, sludge disposal/recovery and also quality control and toxicological involvements became parts of strategical actions at international level. The main disposal strategies for sludge management include agriculture or landscaping purposes, or final disposal. The accepted international policy is sludge application as organic fertilizer in agriculture. In this context, the research paper presents laboratory data used in decisional actions for the sludge land disposal. The study covers physical and chemical characterization of sludge resulted from Focsani WWTP, agriculture soil collected from around of Focsani WWTP and their leachates in compliance with national norms. In addition, the toxic effects on soil organisms (plants) were evaluated. Generally, soil and sludge quality meet the normed criteria for minimizing the potential impact on the environment. The leachate experiments showed the non-hazardous character on the soil properties of groundwater, the predicted impact being insignificant for the tested sludge / soil chemical composition. Ecotoxicological assessment of stabilized sludge showed inhibitory effects in the range of 25% to 100% on seed germination and root growth of plants Sorghum sacharatum, Sinapis alba and Lepidium sativum. In the range of 1% or 5% no significant inhibitory effect of sludge on plants growth was observed. Sorghum sacharatum showed the best growth, but there were no relevant differences between species. A saftey dose of 5% sludge mixed with agriculture soil (250 tonnes per hectare) was established. A monitoring program of sludge / soil quality and also ecotoxic evaluation was recomanded for the saftey of crops growth and health of living organisms including humans.