Petros Gikas

Single and combined effects of nickel (Ni(II)) and cobalt (Co(II)) ions on activated sludge and on other aerobic microorganisms: a review.

Nickel (N(II)) and cobalt (Co(II)) are often encountered in wastewaters. As conventional wastewater treatment may only partially remove nickel and cobalt, a large fraction of the above metals is released to the aquatic environment. Both metals have been identified as micronutrients, at trace concentrations; however, they are both microbial growth inhibitors, at relatively high concentrations. On the other hand, the combined effects (e.g.: growth stimulation or toxicity) of the above metals have been found to differ from the summation of the effects which occur when the metals are applied individually. Moreover, a number of environmental factors (e.g.: pH, biomedium composition, biomass concentration, presence of other heavy metals) can affect the microbial toxicity of the above metallic species. The present review discusses, in a systematic way, the individual and joint effects of the above heavy metals to the growth of microorganisms grown under aerobic conditions, with focus on the growth of activated sludge. Data on multi-metal toxicity are particularly useful in establishing criteria for heavy metal tolerance levels in the environment.

Characteristics and biogas production potential of municipal solid wastes pretreated with a rotary drum reactor.

This study was conducted to determine the characteristics and biogas production potential of organic materials separated from municipal solid wastes using a rotary drum reactor (RDR) process. Four different types of wastes were first pretreated with a commercial RDR system at different retention times (1, 2 and 3 d) and the organic fractions were tested with batch anaerobic digesters with 2.6 g VS L(-1) initial loading. The four types of waste were: municipal solid waste (MSW), a mixture of MSW and paper waste, a mixture of MSW and biosolids, and a mixture of paper and biosolids. After 20 d of thermophilic digestion (50+/-1 degrees C), it was found that the biogas yields of the above materials were in the range of 457-557 mL g VS(-1) and the biogas contained 57.3-60.6% methane. The total solid and volatile solid reductions ranged from 50.2% to 65.0% and 51.8% to 66.8%, respectively. For each material, the change of retention time in the RDR from 1 to 3d did not show significant (alpha=0.05) influence on the biogas yields of the recovered organic materials. Further studies are needed to determine the minimum retention time requirements in the RDR system to achieve effective separation of organic from inorganic materials and produce suitable feedstock for anaerobic digesters.

A mixed integer optimisation approach for integrated water resources management

In areas lacking substantial freshwater resources, the utilisation of alternative water sources, such as desalinated seawater and reclaimed water, is a sustainable alternative option. This paper presents an optimisation approach for the integrated management of water resources, including desalinated seawater, wastewater and reclaimed water, for insular water deficient areas. The proposed mixed integer linear programming (MILP) model takes into account the subdivided regions on the island, the subsequent localised needs for water use (including water quality) and wastewater production, as well as geographical aspects. In addition, the integration of potable and non-potable water systems is considered. The optimal water management decisions, including the location of desalination, wastewater treatment, and reclamation plants, as well as the conveyance infrastructure for desalinated water, wastewater and reclaimed water, are obtained by minimising the annualised total capital and operating costs. Finally, the proposed approach is applied to two Greek islands: Syros and Paros-Antiparos, for case study and scenario analysis.

Sustainable use of water in the Aegean Islands.

Water demands in the Aegean Islands have increased steadily over the last decade as a result of a building boom for new homes, hotels, and resorts. The increase in water demand has resulted in the disruption of past sustainable water management practices. At present, most freshwater needs are met through the use of the limited groundwater, desalinated seawater, and freshwater importation. Wastewater reclamation, not used extensively, can serve as an alternative source of water, for a variety of applications now served with desalinated and imported water. Three alternative processes: desalination, importation, and water reclamation are compared with respect to cost, energy requirements and long-term sustainability. Based on the comparisons made, water reclamation and reuse should be components of any long-term water resources management strategy.

BTEX removal in pilot-scale horizontal subsurface flow constructed wetlands

Abstract Benzene, toluene, ethylbenzene, and xylenes (BTEX) are commonly encountered pollutants. The focus of the present work is on the removal of BTEX using pilot-scale constructed wetlands (CWs). Experiment carried out in three similar pilot-scale horizontal sub-surface flow constructed wetlands with an area of 35 m2 (each), two of which were planted with different macrophytes (Phragmites australis and Typha latifolia), while an unplanted one was used as control. A number of hydraulic tests were carried out using lithium bromide as tracer, to assess the hydraulic residence time. Residence time distributions for the two CWs indicated that the Typha field was characterized by a void volume fraction (porosity) of 0.16 and exhibited more ideal plug flow behavior (Pe = 29.7) compared with the Phragmites field (Pe = 26.7), which had similar porosity. The measured hydraulic residence times in the planted fields were 35.8, 36.7, and 34.1 h for Typha, Phragmites, and unplanted respectively, at wastewater flow r...

Biogas production from municipal solid wastes using an integrated rotary drum and anaerobic-phased solids digester system.

This research was conducted to develop an integrated rotary drum reactor (RDR)-anaerobic-phased solids (APS) digester system for the treatment of municipal solid waste (MSW) to produce biogas energy and achieve waste reduction. A commercial RDR facility was used to provide a 3-d pretreatment and sufficient separation of the organics from MSW and then the organics were digested in a laboratory APS-digester system for biogas production. The organics generated from the RDR contained 50% total solids (TS) and 36% volatile solids (VS) on wet basis. The APS-digester was started at an organic loading rate (OLR) of 3.1 gVS L(-1) d(-1) and operated at three higher OLRs of 4.6, 7.7 and 9.2 gVS L(-1) d(-1). At the OLR of 9.2 gVS L(-1) d(-1) the system biogas production rate was 3.5 L L(-1) d(-1) and the biogas and methane yields were 0.38 and 0.19 L gVS(-1), respectively. Anaerobic digestion resulted in 38% TS reduction and 53% VS reduction in the organic solids. It was found that the total VFA concentration reached a peak value of 15,000 mg L(-1) as acetic acid in the first 3d of batch digestion and later decreased to about 500 mg L(-1). The APS-digester system remained stable at each OLRs for over 100d with the pH in the hydrolysis reactors in the range of 7.3-7.8 and the pH in the biogasification reactor in 7.9-8.1. The residual solids after the digestion had a high heating value of 14.7 kJ gTS(-1).

Integrated Management of Non-conventional Water Resources in Anhydrous Islands

Anhydrous islands are dependent either on non-conventional water resources, such as desalinated seawater or reclaimed water from wastewater, or on water importation from the mainland. The latter option is often expensive and non-sustainable. Desalinated water can be used for potable and non-potable water applications, while reclaimed water can be used for non-potable water applications. Thus all water needs can be satisfied by an optimal blend of desalinated and reclaimed water. It is important to calculate the optimal capacities and locations of seawater desalination plants, wastewater treatment plants and water reclamation plants, and to estimate the water/wastewater conveyance system, in order to minimise water production and distribution costs. Mathematical modelling and optimisation techniques can be employed for calculating the optimum scenario: the satisfaction of all water needs at minimum cost. In this article, we have estimated the water demands taking into account water quality for the anhydrous Greek island of Syros, in the Aegean Sea. Syros has been subdivided into 6 regions, taking into account geographical and population distribution criteria. All water needs are to be satisfied by desalinated seawater and reclaimed water. A mixed-integer linear programming algorithm is used here to calculate the optimal scenario (location and capacities of desalination plants and wastewater treatment and water reclamation plants, as well as the desalinated water, reclaimed water and wastewater conveyance infrastructure needed) by minimising the annualised total cost including capital and operating costs.

Electrical energy production from biosolids: a comparative study between anaerobic digestion and ultra-high-temperature gasification

Biosolids management is one of the most expensive and complicated processes in sanitation engineering. Anaerobic digestion (AD) is often employed for the stabilization of biomass and for energy production, as approximately 50% of the carbon entering the anaerobic digester is recovered as methane (CH4). Gasification has been used recently for the thermal reformation of biosolids to synthesis gas (syngas), which primarily consists of carbon monoxide (CO) and hydrogen (H2). In the present work, the net electrical energy production from biosolids has been calculated, for a typical activated sludge wastewater treatment plant, with an inlet flow rate of 75,708 m3/d (equal to 20 Mgd). The calculations suggest that the ultra-high-temperature gasification (UHTG) system can achieve a net electrical energy output of about 15.40 MJ/kg(dry biosolids), whereas the AD system can achieve values between 8.45 MJ/kg(dry biosolids). The latter values correspond to approximate net electrical energy power of 18.8 kW for UHTG, versus 9.9 kW for AD, for a wastewater treatment plant with capacity of 1000 m3/d; thus, the UHTG process yields approximately 190% of the energy that may be produced by the AD process.

An Optimisation-based Approach for Integrated Water Resources Management

This paper considers an integrated water management problem for a region lacking fresh and ground water resources, which comprises (a) the optimal placement of desalination, water reclamation and wastewater treatment plants, (b) the calculation of the optimal capacities of the above facilities, and (c) the calculation of the optimal conveyance system for desalinated, reclaimed water and wastewater. This problem is formulated as a mixed-integer linear programming (MILP) model, with an objective to minimise the annualised total cost including capital and operating costs. Finally, the proposed model is applied to a real case for the Greek island of Syros in the Aegean Sea.

Near zero energy wastewater treatment plants for the Greek islands.

AbstractConventional wastewater treatment is an energy-intensive process, requiring electric energy of about 1.1–2.4 MJ/m3, being higher in plants with relatively small hydraulic capacity (<5,000 m3/d). Solar energy can be used to supply electric energy, particularly for the Greek islands; however, the huge energy demand of the wastewater treatment is a drawback for the use of photovoltaic energy, due to the additional capital cost and electricity storage requirements during the night. Here, a novel approach for wastewater treatment is proposed, based on enhanced primary solids removal, by the use of advanced sieving and filtration processes, utilizing a proprietary rotary fabric belt microscreen followed by a proprietary continuous backwash upflow media filter. Raw municipal wastewater treated with the above process results in about 80–90% reduction in TSS and 60–70% reduction in BOD5. The overall electrical power requirements for a novel configuration plant with hydraulic capacity of 1,000 m3/d (typical...