Katherine J. Haralambous

Industrial wastewater pre-treatment for heavy metal reduction by employing a sorbent-assisted ultrafiltration system

This work examined the adoption of a sorbent-assisted ultrafiltration (UF) system for the reduction of Pb(II), Cu(II), Zn(II) and Ni(II) from industrial wastewater. In such a system metals were removed via several processes which included precipitation through the formation of hydroxides, formation of precipitates/complexes among the metal ions and the wastewater compounds, adsorption of metals onto minerals (bentonite, zeolite, vermiculite) and retention of insoluble metal species by the UF membranes. At pH=6 the metal removal sequence obtained by the UF system was Pb(II)>Cu(II)>Zn(II)>Ni(II) in mg g⁻¹ with significant amount of lead and copper being removed due to chemical precipitation and formation of precipitates/complexes with wastewater compounds. At this pH, zinc and nickel adsorption onto minerals was significant, particularly when bentonite and vermiculite were employed as adsorbents. Metal adsorption onto zeolite and bentonite followed the sequence Zn(II)>Ni(II)>Cu(II)>Pb(II), while for vermiculite the sequence was Ni(II)>Zn(II)>Cu(II)>Pb(II) in mg g⁻¹. The low amount of Pb(II) and Cu(II) adsorbed by minerals was attributed to the low available lead and copper concentration. At pH=9 the adoption of UF could effectively reduce heavy metals to very low levels. The same was observed at pH=8, provided that minerals were added. The prevailing metal removal process was the formation of precipitates/complexes with wastewater compounds.

REMOVAL OF HEAVY METALS FROM SEWAGE SLUDGE BY ACID TREATMENT

Sludge samples were found to contain significant amounts of heavy metals (Cr, Cu, Ni, Pb and Zn) and were subjected to acid treatment using either hydrochloric, sulfuric, nitric or phosphoric acid. The optimum combination, in terms of metal removal efficiency and environmental impacts was sought through a variety of tests by applying a ratio of 1:5 of sludge quantity (g) per volume of acid (ml). The concentrations of the different acids used, were in the range of 5%–20% and the contact times ranged between 15 and 60 minutes. The optimum combination was achieved when the sludge samples were in contact with H2SO4 20%v/v for 60 minutes. In order to estimate the metal leachability, the heavy metal content as well as the metal distribution in the residue were investigated and it was found that most of the heavy metal content was extracted while the remaining was removed from the initial mobile phases to the more stable ones.

Regeneration of natural zeolite polluted by lead and zinc in wastewater treatment systems

The aim of this work was to investigate the potential regeneration of natural zeolite which had been contaminated with lead and zinc contained in aqueous solutions, treated secondary effluent and primary treated wastewater. Several desorbing solutions were examined for the removal of Pb(II) and Zn(II) from zeolite and the highest desorption efficiency was obtained for 3M KCl and 1M KCl, respectively. The desorption process depended on the type and concentration of the desorbing solution, the metal being desorbed, the mineral selectivity towards the metal and the composition of the liquid medium where the adsorption process had taken place. Successive regeneration cycles resulted in the reduction of desorption efficiency by more than 50% after 9 and 4 cycles for lead and zinc, respectively. Kinetics examination showed that desorption was slower than adsorption, while metal ions which had been easily adsorbed were difficult to be desorbed. Adsorption was characterized by a three-stage diffusion process, while desorption followed a two-stage diffusion process.

Natural zeolites and their ion exchange behavior towards chromium

Abstract In this work studies have been performed which demonstrate that trivalent chromium cations may be retained by naturally occuring zeolites. The experimental work perfomed on the natural zeolite clinoptilolite, which is found in abudant quantities in Greece, showed that the ion exchange process is quite rapid and high quantities of chromium ions are removed from the aqueous solutions in a short period of time. Also, the actual exchange capacity of the zeolites is much smaller, about 50%, of the theoretical one. Despite the regeneration conditions used, significant amounts of chromium is retained by the zeolite. It was also shown that loading and regenerating the zeolite greatly improves the ion exchange capacity of the zeolite, since a very small amount of chromium is released during regeneration and an almost constant amount is taken after each loading cycle.

Examination of zinc uptake in a combined system using sludge, minerals and ultrafiltration membranes.

This work investigates the feasibility of zinc removal from wastewater with the use of ultrafiltration (UF) membranes combined with natural minerals and sludge. Activated sludge obtained from a membrane bioreactor (MBR) was enriched with initial zinc concentration of 320 mg/L and specific concentrations of zeolite, bentonite and vermiculite. The mixture was agitated and placed inside a batch ultrafiltration unit where the filtration process took place. The effect of several parameters on zinc removal was investigated including the mineral type, quantity and grain size, the metal-mineral contact time and the associated kinetics, the pH value, the zinc initial concentration and sludge mixed liquor suspended solids (MLSS) concentration. The ultrafiltration membranes without any mineral addition were able to remove 38-78% of zinc ions due to biosorption on sludge flocs. The addition of minerals increased the Zn(II) removal efficiencies reaching in some cases more than 90%. Bentonite was the most effective mineral in zinc removal followed by vermiculite. Alkaline pH values favoured zinc removal due to enhanced chemical precipitation. A three-stage adsorption process was identified where the boundary layer diffusion process was followed by a two-stage intraparticle diffusion process. Powder size vermiculite was more effective than granular vermiculite in zinc removal. Minerals also resulted in membrane fouling mitigation since the membrane permeability drop was reduced. The combined sludge-mineral-ultrafiltration system can be effectively employed for the treatment of industrial wastewater.

Studies on the nickel removal from aqueous solutions

Abstract Studies have been performed which demonstrate the influence of several anions on the removal of nickel cations from aqueous solutions by means of natural clinoptilolite. The experimental work performed showed that the ion exchange process is a fast process for both the ammonium and sodium converted clinoptilolite.The actual exchange capacity of sodium clinoptilolite was found lower compared to that of the ammonium clinoptilolite. Nickel removal was higher in the presence of nitrate anions followed by sulfate and chloride anions. For the Watt type electroplating solution the nickel was effectively removed by combining precipitation and ion exchange, the best results obtained with ammonium clinoptilolite.

Leaching properties of slag generated by a gasification/vitrification unit: The role of pH, particle size, contact time and cooling method used

The environmental impact from the operation of thermal waste treatment facilities mainly originates from the air emissions, as well as the generated solid residues. The objective of this paper is to examine the slag residue generated by a demonstration plasma gasification/vitrification unit and investigate the composition, the leaching properties of the slag under different conditions, as well as the role of the cooling method used. The influence of pH, particle size and contact time on the leachability of heavy metals are discussed. The main outcome is that the vitrified slag is characterized as inert and stable and can be safely disposed at landfills or used in the construction sector. Finally, the water-cooled slag showed better resistance in relation to heavy metal leachability compared to the air-cooled slag.

Application of Adsorption and Ultrafiltration Processes for the Pre-treatment of Several Industrial Wastewater Streams

In this work ultrafiltration (UF) was coupled with suitable minerals and dried activated sludge for the pre-treatment of several industrial wastewater streams. The aim was to decrease heavy metal concentrations to low levels so that wastewater can be safely discharged into municipal sewers or biological wastewater treatment can take place without biomass inhibition problems. Industrial wastewater originating from metal plating, chemical and textile industries was employed. The experiments were conducted in a reactor where the UF membrane module was immersed. UF reduced the amount of heavy metals, but the performance was variable with removal efficiencies ranging from 20 to 99.7xa0%, depending on the metal type and on the wastewater initial characteristics. The prevailing wastewater characteristics were the pH, the presence of certain anions, the suspended solids concentration and the presence of competing cations. The addition of activated sludge and/or minerals could further increase heavy metal removal through the process of sorption. UF assisted by minerals could achieve variable colour and COD removal ranging from 22 to 94xa0% and 58 to > 99.9xa0% respectively. Minerals resulted in membrane fouling mitigation, while sludge adversely impacted on fouling.

Investigation of the inhibitory effects of heavy metals on heterotrophic biomass activity and their mitigation through the use of natural minerals

This study examined the inhibitory effects of lead, copper, nickel and zinc on heterotrophic biomass and their potential mitigation through the use of low-cost, natural minerals. Activated sludge was placed in batch reactors and specific heavy metal concentrations were added. Subsequently, the biomass specific oxygen uptake rate (sOUR) was determined to assess the level of biomass inhibition. Biomass inhibition by heavy metals followed the order Cu2+>Pb2+>Zn2+>Ni2+, with copper being the most toxic metal, causing high inhibition of heterotrophic biomass even at relatively low concentrations (i.e. 10 mg·L−1). Zn had very small toxic effect at 10 mg·L−1, while at 40 mg·L−1 the level of biomass inhibition reached 80%. Nickel stimulated activated sludge activity at concentrations of the order of 10 mg·L−1. The addition of 10 g·L−1 bentonite and zeolite in activated sludge resulted in the decrease of the inhibitory effect of heavy metals on biomass respiratory activity. In some cases, mineral addition was very favorable as inhibition was reduced from 69–90% to less than 55% and even up to 12%. The beneficial action of minerals is attributed both to the adsorption of heavy metals on the mineral and on the potential aggregation between mineral and sludge particles.

Development of guidelines on best practices for the slaughter of animals in Cyprus.

Cyprus is one of the candidate countries to become a full member of the European Union. In order to access formally to the EU, Cyprus has to follow an implementation process and take into account all the obligations that the fifteen Member States have to respect. A large number of obligations derive from the European Integrated Pollution Prevention and Control (IPPC) Directive 96/61/EC, which intends to result in the protection of the environment as a whole and the public health as well. This will be the outcome of determining ways of pollution prevention and control for several industrial sectors, which are covered by the IPPC Directive and then taking action so that all operators act according to the Directives demands. In this framework, the National Technical University of Athens, after thorough examination of a large number of documents relevant to the Best Available Techniques (BATs), developed guidelines for the application of BATs for 14 categories of the industry of Cyprus. This paper concerns the developed guidelines for slaughterhouses.