Simos Malamis

Fractionation of proteins and carbohydrates of extracellular polymeric substances in a membrane bioreactor system.

The major operational problem associated with membrane bioreactors (MBR) is membrane fouling, for which extracellular polymeric substances (EPS) are primarily responsible. In this work both the soluble and bound EPS (i.e. SMP and EPS) produced in an MBR system operating under sludge retention times (SRT) of 10, 15, 20 and 33 days were fractionized by means of membranes having variable molecular weight cutoffs (300 kDa, 100 kDa, 10 kDa & 1 kDa). The results show that increasing the SRT leads to a reduction of SMP and EPS and that these reductions are more pronounced for the SRTs in the range 10-20 days. This reduction is more significant for carbohydrates than for proteins. The decrease of SMP and EPS with increasing SRT from 10 to 20 days led to a significant decrease of the level of fouling. The further increase of SRT to 33 days did not significantly impact on the level of fouling as the SMP and EPS concentrations did not change much. Under the examined operating conditions, EPS were found to be composed mainly of large macromolecules having a size of 0.45 microm-300 kDa and to a lower extent of very small molecules (<1 kDa) that are not easily decomposed by the biomass activity. The majority of SMP is composed of very small molecules (<1 kDa), while some macromolecules in the range of 0.45 microm-300 kDa are present. Consequently, both EPS and SMP were found to have a bimodal character.

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.

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.

Performance of a membrane bioreactor used for the treatment of wastewater contaminated with heavy metals

In this work the performance of a Membrane bioreactor (MBR) was assessed for the removal of 3-15 mg/l of copper, lead, nickel and zinc from wastewater. The average removal efficiencies accomplished by the MBR system were 80% for Cu(II), 98% for Pb(II), 50% for Ni(II) and 77% for Zn(II). The addition of 5 g/l vermiculite into the biological reactor enhanced metal removal to 88% for copper, 85% for zinc and 60% for nickel due to adsorption of metal ions on the mineral, while it reduced biomass inhibition and increased biomass growth. The metal ions remaining in soluble form penetrated into the permeate, while those attached to sludge flocs were effectively retained by the ultrafiltration membranes. The average heterotrophic biomass inhibition was 50%, while it reduced to 29% when lower metal concentrations were fed into the reactor in the presence of vermiculite. The respective autotrophic biomass inhibition was 70% and 36%. The presence of heavy metals and vermiculite in the mixed liquor adversely impacted on membrane fouling.

Assessment of metal removal, biomass activity and RO concentrate treatment in an MBR–RO system

This work investigated the removal of metals from wastewater using a combined Membrane Bioreactor-Reverse Osmosis (MBR-RO) system. The concentrate produced by the RO system was treated by a fixed bed column packed with zeolite. The average metal removal accomplished by the MBR treating municipal wastewater was Cu(90%), Fe(85%), Mn(82%), Cr(80%), Zn(75%), Pb(73%), Ni(67%), Mg(61%), Ca(57%), Na(30%) and K(21%), with trivalent and divalent metals being more effectively removed than monovalent ones. The metal removal achieved by the MBR system treating wastewater spiked with Cu, Pb, Ni and Zn (4-12 mg L(-1) of each metal) was Pb(96%)>Cu(85%)>Zn(78%)>Ni(48%). The combined MBR-RO system enhanced metal removal from municipal wastewater to the levels of >90.9->99.8%, while for wastewater spiked with heavy metals the removal efficiencies were >98.4%. Fixed bed column packed with zeolite was effective for the removal of Cu, Pb and Zn from the RO concentrate, while Ni removal was satisfactory only at the initial stages of column operation. The presence of heavy metals increased inorganic fouling.

A review on nitrous oxide (N2O) emissions during biological nutrient removal from municipal wastewater and sludge reject water

Nitrous oxide (N2O) is an important pollutant which is emitted during the biological nutrient removal (BNR) processes of wastewater treatment. Since it has a greenhouse effect which is 265 times higher than carbon dioxide, even relatively small amounts can result in a significant carbon footprint. Biological nitrogen (N) removal conventionally occurs with nitrification/denitrification, yet also through advanced processes such as nitritation/denitritation and completely autotrophic N-removal. The microbial pathways leading to the N2O emission include hydroxylamine oxidation and nitrifier denitrification, both activated by ammonia oxidizing bacteria, and heterotrophic denitrification. In this work, a critical review of the existing literature on N2O emissions during BNR is presented focusing on the most contributing parameters. Various factors increasing the N2O emissions either per se or combined are identified: low dissolved oxygen, high nitrite accumulation, low chemical oxygen demand to nitrogen ratio, slow growth of denitrifying bacteria, uncontrolled pH and temperature. However, there is no common pattern in reporting the N2O generation amongst the cited studies, a fact that complicates its evaluation. When simulating N2O emissions, all microbial pathways along with the potential contribution of abiotic N2O production during wastewater treatment at different dissolved oxygen/nitrite levels should be considered. The undeniable validation of the robustness of such models calls for reliable quantification techniques which simultaneously describe dissolved and gaseous N2O dynamics. Thus, the choice of the N-removal process, the optimal selection of operational parameters and the establishment of validated dynamic models combining multiple N2O pathways are essential for studying the emissions mitigation.

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.

Copper removal from sludge permeate with ultrafiltration membranes using zeolite, bentonite and vermiculite as adsorbents

The aim of this work is to examine copper removal from sludge permeate with the use of low-cost minerals of Mediterranean origin combined with ultrafiltration membranes. The minerals used were zeolite (clinoptilolite), bentonite and vermiculite. Activated sludge was enriched with 0.01 N (317.7 ppm) of Cu(II). Fixed concentrations of minerals were added to sludge and the pH value was adjusted at 5.5. The mixture was agitated for 2 hours at 800 rpm at room temperature and was then filtered through a batch ultrafiltration system for 1 hour. This experiment was repeated, for comparison purposes, with sludge enriched with 0.01 N of Cu(II) with no mineral addition. The results showed that ultrafiltration membranes with no mineral addition were able to remove a significant amount of copper with removal efficiencies ranging from 59.4-78.3%. The addition of 10 g/l and 20 g/l of bentonite combined with ultrafiltration membranes resulted in removal efficiencies of 94.9% and 99.4% respectively and that of 10 g/l and 20 g/l of vermiculite in removal efficiencies of 93.8% and 96.8%, respectively. The ion exchange capacity of minerals followed the order bentonite > vermiculite > zeolite. Furthermore, membrane fouling was investigated. The addition of zeolite and bentonite reduced membrane fouling, while the addition of vermiculite did not impact on fouling. The use of low-cost minerals in combination with ultrafiltration membranes can be employed to treat industrial wastewater, resulting in a final effluent with very low copper concentrations.

Development of a Novel Process Integrating the Treatment of Sludge Reject Water and the Production of Polyhydroxyalkanoates (PHAs)

Polyhydroxyalkanoates (PHAs) from activated sludge and renewable organic material can become an alternative product to traditional plastics since they are biodegradable and are produced from renewable sources. In this work, the selection of PHA storing bacteria was integrated with the side stream treatment of nitrogen removal via nitrite from sewage sludge reject water. A novel process was developed and applied where the alternation of aerobic-feast and anoxic-famine conditions accomplished the selection of PHA storing biomass and nitrogen removal via nitrite. Two configurations were examined: in configuration 1 the ammonium conversion to nitrite occurred in the same reactor in which the PHA selection process occurred, while in configuration 2 two separate reactors were used. The results showed that the selection of PHA storing biomass was successful in both configurations, while the nitrogen removal efficiency was much higher (almost 90%) in configuration 2. The PHA selection degree was evaluated by the volatile fatty acid (VFA) uptake rate (-qVFAs) and the PHA production rate (qPHA), which were 239 ± 74 and 89 ± 7 mg of COD per gram of active biomass (Xa) per hour, respectively. The characterization of the biopolymer recovered after the accumulation step, showed that it was composed of 3-hydroxybutyrate (3HB) (60%) and 3-hydroxyvalerate (3HV) (40%). The properties associated with the produced PHA suggest that they are suitable for thermoplastic processing.

Inhibition of biomass activity in the via nitrite nitrogen removal processes by veterinary pharmaceuticals.

The inhibitory effect of two veterinary pharmaceuticals was studied for different types of biomass involved in via nitrite nitrogen removal processes. Batch tests were conducted to determine the inhibition level of acetaminophen (PAR) and doxycycline (DOX) on the activity of short-cut nitrifying, denitrifying and anoxic ammonium oxidation (anammox) biomass and phosphorus accumulating organisms (PAOs). All biomass types were affected by PAR and DOX, with anammox being the most sensitive bacteria. DOX inhibited more the biomass treating high strength nitrogenous effluents (HSNE) than low strength nitrogenous effluents (LSNE). The phosphorus uptake inhibition under anoxic conditions was lower than 25% in the presence of PAR up to 400 mg L(-1). The same DOX concentration inhibited anoxic phosphorus uptake more than 65% for biomass treating LSNE and HSNE. Heterotrophic denitrifying bacteria seem to be more robust at high DOX and PAR concentrations than anammox. Both veterinary products inactivated ammonium oxidizing, Accumulibacter phosphatis and denitrifying bacteria.