Martina Piredda

Biodegradability and Toxicity of Pharmaceuticals in Biological Wastewater Treatment Plants

In this experimental study both biological treatability of pharmaceuticals and their potential toxic effect in biological processes were evaluated. The pharmaceuticals were selected among those that are present at higher concentration in the Italian wastewater treatment plant effluents and widely used as antiulcer (ranitidine), β-blocker (atenolol) and antibiotic (lincomycin). The present paper is the continuation of a work already presented,[1] which used a synthetic wastewater fed to laboratory scale SBR (Sequencing Batch Reactor) operated with different sludge ages (8 and 14 days), different biochemical conditions (aerobic or anoxic-aerobic mode) and several influent drug concentrations (2, 3 and 5 mg/L). In this case a real municipal wastewater was used as influent to the SBR. In parallel, batch tests were conducted to determine the removal kinetics of drugs and nitrogen. Toxicity tests using a titrimetric biosensor to verify possible inhibition on microorganisms were also performed. Finally, the possible adsorption of the pharmaceuticals on activated sludge was evaluated. The drugs under investigation showed different behaviours in terms of both biodegradability and toxicity effect on nitrifiers. Ranitidine showed generally low removal efficiencies (17–26%) and a chronic inhibition on nitrification. Atenolol showed generally higher removal efficiencies than ranitidine, even if the fairly good efficiency obtained in the previous experimentation with synthetic wastewater (up to 90%) was not attained with real wastewater (36%). No inhibition on nitrification was observed on both acclimated and non acclimated microorganisms with a high nitrification activity, whilst it was present with activated sludge characterised by a lower nitrification activity. Consistently with his pharmaceutical properties, lincomycin showed significant inhibition on nitrification activity.

Acetate-fed aerobic granular sludge for the degradation of 4-chlorophenol.

Chlorinated phenols are considered a critical environmental problem, due to their extreme toxicity and their widespread use both in industrial and agricultural activities. In this study, aerobic granular sludge was initially developed into an acetate-fed Granulated Sequencing Batch Reactor (GSBR) and then used for the degradation of low chlorinated 4-mono-chlorophenol (4CP), with readily biodegradable sodium acetate (NaAc) as co-substrate. Influent 4CP concentration ranged between 0 and 50mg/l, with a maximum volumetric organic loading rate of 0.20 kg(4CP)/m(3)d (0.32 kg(COD-4CP)/m(3)d). Differences in granules shape and size were observed with 4CP dosed in the influent at different concentrations, and the effects of such toxic compound on acetate removal were evaluated, with both unacclimated and acclimated biomass. Aerobic granules grown on acetate as carbon source proved to be an interesting solution for the degradation of 4CP, showing good resistance to high 4CP concentrations in the influent even if unacclimated (short term effects). Moreover, the monitoring of intermediate products and the evaluation of chloride release due to 4CP degradation proved that acclimated granular sludge could completely remove 4CP (long term effects), with high specific removal rates.

Application of accelerated carbonation on MSW combustion APC residues for metal immobilization and CO2 sequestration.

The present study focuses on the application of an aqueous phase accelerated carbonation treatment on air pollution control (APC) residues from municipal solid waste combustion, aimed at assessing its influence on the environmental behaviour of the residue under concern, as well as the potential of the process in terms of sequestration of the CO2. APC residues are considered hazardous waste and must be treated before final disposal in order to achieve the immobilization/mobilization of critical contaminants such as heavy metals as well as mobilization of soluble salts. The treatment applied proved to be effective in reducing the mobility of Pb, Zn, Cr, Cu and Mo, the optimum final pH for the carbonated APC residues being in a range of 10-10.5, whilst a mobilization effect was noticed for Sb and no effect was assessed for chlorides. The effect of carbonation treatment on the contaminant release was further evaluated by means of a sequential extraction procedure, indicating that the distribution of contaminants on water soluble, exchangeable and carbonate fraction was modified after treatment. The CO2 sequestration potential assessed for the APC residues showed that the carbonation technology could be a technically viable option in order to reduce emissions from WtE plants.

Acetate-fed aerobic granular sludge for the degradation of chlorinated phenols

In this study, the possibility to use acetate-fed aerobic granular sludge for the degradation of low chlorinated 4-mono-chlorophenol (4CP) and highly chlorinated 2,4,6-tri- chlorophenol (TCP) was investigated. A Granulated Sequencing Batch Reactor (GSBR) was used to carry out the experiments, with acetate as growth substrate. 4CP concentration in the influent ranged between 0 and 50 mg/l, while TCP concentration varied between 0 and 15 mg/l. Different operating conditions were applied in order to obtain the complete aerobic degradation of 4CP. For TCP degradation, anaerobic feeding and control of dissolved oxygen concentration in the bulk liquid were used to keep the granules core under anaerobic conditions due to diffusion limitations: the possibility to obtain TCP reductive dechlorination under aerated conditions was thus investigated. Differences in granules shape and size were observed with 4CP and TCP dosed in the influent, and the effects of such toxic compounds on acetate removal were evaluated.Aerobic granules grown on acetate as carbon source proved to be an interesting solution for the degradation of 4CP, showing good resistance to high 4CP concentrations in the influent even if unacclimated. The presence of TCP did not irreversibly inhibit biomass activity, and complete TCP degradation was achieved after acclimation.

Biomass ash reutilisation as an additive in the composting process of organic fraction of municipal solid waste

In this work the effects of selected types of biomass ash on the composting process and final product quality were studied by conducting a 96-day long experiment where the source separated organic fraction of municipal waste, mixed with wood prunings that served as bulking agent, was added with 0%, 2%, 4% and 8% wt/wt of biomass ash. The evolution over time of the main process parameters was observed, and the final composts were characterised. On the basis of the results, both the composting process and the quality of the final product were improved by ash addition. Enhanced volatile solids reduction and biological stability (up to 32% and 52%, respectively, as compared to the unamended product) were attained when ash was added, since ash favored the aerobic degradation by acting asa physical conditioner. In the final products, higher humification of organic matter (expressed in terms of the humification index, that was 2.25 times higher in the most-enriched compost than in the unamended one) and total Ca, K, Mg and P content were observed when ash was used. The latter aspect may influence the composts marketability positively, particularly with regards to potassium and phosphorus. The heavy metals content, that is regarded as the main environmental disadvantage when using ash asa composting additive, did not negatively affect the final composts quality. However, some other controversial effects of ash, related to the moisture and temperature values attained during the process, pH (8.8-9.2 as compared to 8.2 of the unamended compost) and electrical conductivity levels (up to 53% higher as compared to the unamended compost) in the final composts, were also observed.