C.A. Papadimitriou

Comparative study of phenol and cyanide containing wastewater in CSTR and SBR activated sludge reactors.

The objectives of this work were the examination of the performance of two bench scale activated sludge systems, a conventional Continuous Stirring Tank Reactor (CSTR) and a Sequential Batch Reactor (SBR), for the treatment of wastewaters containing phenol and cyanides and the assessment of the toxicity reduction potential by bioassays. The operation of the reactors was monitored by physicochemical analyses, while detoxification potential of the systems was monitored by two bioassays, the marine photobacterium Vibrio fischeri and the ciliate protozoan Tetrahymena thermophila. The reactors influent was highly toxic to both organisms, while activated sludge treatment resulted in the reduction of toxicity of the influent. An increased toxicity removal was observed in the SBR; however CSTR system presented a lower ability for toxicity reduction of influent. The performance of both systems was enhanced by the addition of powdered activated carbon in the aeration tank; activated carbon upgraded the performance of the systems due to the simultaneous biological removal of pollutants and to carbon adsorption process; almost negligible values of phenol and cyanides were measured in the effluents, while further toxicity reduction was observed in both systems.

An investigation on the physical, chemical and ecotoxicological characteristics of particulate matter emitted from light-duty vehicles

Particulate matter (PM) emitted from three light-duty vehicles was studied in terms of its physicochemical and ecotoxicological character using Microtox bioassay tests. A diesel vehicle equipped with an oxidation catalyst emitted PM which consisted of carbon species at over 97%. PM from a diesel vehicle with a particle filter (DPF) consisted of almost equal amounts of carbon species and ions, while a gasoline vehicle emitted PM consisting of approximately 90% carbon and approximately 10% ions. Both the DPF and the gasoline vehicles produced a distinct nucleation mode at 120 km/h. The PM emitted from the DPF and the gasoline vehicles was less ecotoxic than that of conventional diesel, but not in direct proportion to the emission levels of the different vehicles. These results indicate that PM emission reductions are not equally translated into ecotoxicity reductions, implying some deficiencies on the actual environmental impact of emission control technologies and regulations.

Effect of hexavalent chromium on the activated sludge process and on the sludge protozoan community.

The objectives of this study were the determination of chromium effects to the performance of an activated sludge unit and the investigation of the response of the activated sludge protozoan community to Cr(VI). Two bench scale activated sludge reactors were supplied with synthetic sewage containing Cr(VI), at concentrations from 1 up to 50 mg L(-1). Protozoan species were identified and were related to the system efficiency. Variations in the abundance and diversity of the protozoan species were observed under various chromium concentrations. High removal rates of organics and nutrients were observed after the acclimatization of the activated sludge, which were related to the initial chromium(VI) concentration. Chromium(VI) removal efficiency was high in all cases. The protistan community was affected by the influent chromium content. Dominance of sessile species was observed in the reactor receiving 5 mg L(-1) influent chromium, whereas co-dominance of sessile and carnivorous species was observed in the reactors receiving higher chromium concentrations.

Comparison of several toxicity tests applied to complex wastewaters and mussel biomarkers in receiving waters

In this study, the complex wastewaters/effluents discharged to coastal regions of Turkey and Greece were sampled, and various toxicity tests were applied. The bioassays used included the assessment of the luminescence inhibition of the bacterium Vibrio fisheri, the photosynthesis inhibition (14C uptake rate) and growth inhibition of the algal species Phaeodactylum tricornutum, and the mortality of the crustacean Artemia franciscana and rotifer Brachionus plicatilis. Additionally, “neutral red retention” and “filtration rate” sublethal biomarker techniques were performed by utilizing the mussel species Mytilus galloproviancialis, inhabiting the points of discharges in Turkey. All discharges tested were found to be acutely toxic to P. tricornutum and slightly toxic to V. fisheri, A. franciscana, and B. plicatilis. Test results showed that the 14C uptake rate toxicity test was the most sensitive one among the other bioassays. The biomarker results showed that the health status of mussels in the coastal areas decreased significantly, indicating the pollution of the receiving waters in Turkey. The conclusions drawn highlight the necessity for an intesive ecotoxicological monitoring scheme that will incorporate the most suitable bioassays and biomarkers to adequately contribute to the upgrading and maintenance of the ecological quality of the coastal waters in Greece and in Turkey. *Presented as an invited plenary lecture at “The 2nd Asian International Conference on Ecotoxicology and Environmental Safety” (SECOTOX 2004), Songkla, Thailand, 26–29 September 2004.

Protozoans as indicators of sequential batch processes for phenol treatment; an autoecological approach.

The objective of this study was the investigation of the potential use of protistan species as quality indicators of the activated sludge performance in sequential batch processes receiving toxic compounds. Two laboratory scale sequential batch reactors (SBR) were used, a conventional one and a system with plastic biofilm carriers (SBBR), treating wastewater containing phenol at concentrations ranging from 1 up to 40 mg/L. Physicochemical analyses of the samples included the determination of MLSS, effluent suspended solids, BOD5, nitrogen-ammonia, nitrogen-nitrate and phenol. The activated sludge protistan community was identified and enumerated in each reactor. Statistical analyses included Canonical Correspondence Analysis and Indicator Species Analysis of the collected experimental data. Canonical Correspondence Analysis showed inversely proportional relationships between the protozoa and the physicochemical parameters of the effluent as well as protozoan species competition. Indicator species analysis revealed the presence and the prevalence of different species under various phenol influent concentrations. No indicator species were observed for the period of operation under 5 mg/L influent phenol in both reactors, while no indicator species were observed for 20 mg/L influent phenol in the SBR reactor. Carchesium and Epistylis sp. showed the higher values for 1 mg/L phenol in the SBR, while Holophrya sp. showed lower indicator values for the same period in the SBBR. Although several species showed a good correlation to the treatment efficiency of the reactors, Blepharisma sp., could be used as the primary indicator species in both reactors for the operation period under 40 mg/L phenol, as deduced by statistical analysis.

Study of phytotoxic properties of sewage sludge stabilised by alkaline mediums

The aim of this work was the examination of the stabilization potential of sewage sludge by fly ash and lime and the investigation of the phytotoxic properties of the produced mixtures. About 0,5 m sewage sludge were mixed with the alkaline substances in various ratios and the products were stabilized for 3 months. Samples from each mixture were analyzed for the determination of their physicochemical content such as pH, moisture, and nutrients. Stabilization of sewage sludge was achieved depending upon the concentration and the type of alkaline medium, due to the pH increase of the mixture; however, the alkaline addition resulted in the reduction of the nutrients content. Phytotoxicity effects were determined by the measurement of the corresponding inhibition effects of the produced mixtures on the seed germination and root length growth of three higher plants (one monocotyl and two dicotyls). Samples obtained from the early stages of stabilization process exhibited high inhibition on seed germination and root length growth; however, these effects were reduced for samples prepared at extended stabilization times.