Constantinos Noutsopoulos

Anaerobic co-digestion of grease sludge and sewage sludge: The effect of organic loading and grease sludge content

The objective of this study was to assess the feasibility of co-digesting grease sludge (GS) originating from domestic wastewater along with sewage sludge (SS) and to assess the effect of organic loading rate (OLR) and GS content on process performance. Three lab-scale semi-continuous fed mesophilic anaerobic digesters were operated under various OLRs and SS-GS mixtures. According to the results, addition of GS up to 60% of the total VS load of feed resulted in a 55% increase of biogas yield (700 vs. 452m(3)/tVSadded) for an OLR of 3.5kg VS/m(3)/d. A stable and satisfactory operation of anaerobic co-digestion units can be achieved for a GS-OLR up to 2.4kg VSGS/m(3)/d. For such values biogas yield is linearly proportional to the applied GS-OLR, whereas biogas yield is minimal for GS-OLR higher than this limit and acidification of the anaerobic digestion units is taking place.

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.

Biological groundwater treatment for chromium removal at low hexavalent chromium concentrations

The objective of this work is to develop and evaluate biological groundwater treatment systems that will achieve hexavalent chromium reduction and total chromium removal from groundwater at hexavalent chromium (Cr(VI)) groundwater concentrations in the 0-200 μg/L range. Three lab-scale units operated, as sequencing batch reactors (SBR) under aerobic, anaerobic and anaerobic-aerobic conditions. All systems received groundwater with a Cr(VI) content of 200 μg/L. In order to support biological growth, groundwater was supplemented with milk, liquid cheese whey or a mixture of sugar and milk to achieve a COD concentration of 200 mg/L. The results demonstrate that a fully anaerobic system or an anaerobic-aerobic system dosed with simple or complex external organic carbon sources can lead to practically complete Cr(VI) reduction to Cr(III). The temperature dependency of maximum Cr(VI) removal rates can be described by the Arrhenius relationship. Total chromium removal in the biological treatment systems was not complete because a significant portion of Cr(III) remained in solution. An integrated system comprising of an anaerobic SBR followed by a sand filter achieved more than 95% total chromium removal thus resulting in average effluent total and dissolved chromium concentrations of 7 μg/L and 3 μg/L, respectively.

Removal of endocrine disruptors and non-steroidal anti-inflammatory drugs through wastewater chlorination: The effect of pH, total suspended solids and humic acids and identification of degradation by-products

Endocrine disrupting chemicals (EDCs) and non-steroidal anti-inflammatory drugs (NSAIDs) are two groups of emerging pollutants the significance of which rests on their persistent detection in the aquatic environment and their possible adverse effects. Wastewater treatment plants are one of the major ways for transporting such chemicals in the aquatic environment. Chlorination is usually the last stage of treatment before wastewater being disposed to the aquatic environment. This work focuses on the evaluation of the effect of chlorine dose and specific wastewater characteristics (pH, total suspended solids and humic acids) on the removal of target EDCs and NSAIDs through chlorination. Another objective of this study is the identification of chlorination by-products of specific EDCs and NSAIDs and their dependence on contact time. Based on the results it is concluded that the effect of chlorine dose and humic acids concentration on the degradation of target compounds during chlorination is minimal. On the contrary, pH is a critical parameter which highly affects process performance. Moreover, it is concluded that not only the free available chlorine species, but also the properties of EDCs and NSAIDs under different pH conditions can affect chlorination process performance. The effect of TSS on the degradation of the target compounds during chlorination is more profound for chemicals with high Kow values and therefore higher affinity to partition to the particulate phase (i.e. nonylphenols, triclosan). Several degradation by-products were identified through chlorination of nonylphenol, bisphenol A and diclofenac. The dependence of these by-products on chlorination contact time is also demonstrated.

Identification of type and causes of filamentous bulking under mediterranean conditions

A national survey to identify the most common filamentous microorganisms in Greek wastewater treatment plants, to assess the extent of filamentous bulking phenomenon and to correlate the occurrence of these bacteria to specific operating parameters, was carried out for five years. According to the conclusions of this survey filamentous bulking is a widespread phenomenon in Greek wastewater treatment plants. Almost 70% of the sludge samples examined exhibited filament indices greater than 4 during the winter period. The most common filamentous species found in a decreasing order were M. parvicella, Type 0092, GALOs, Type 0041 and N. limicola. A seasonal variation of the composition of the biomass was observed. M. parvicella is the dominant species during winter periods, while T0092 is the dominant species during summer conditions. This seasonal pattern of biomass composition was followed by a similar seasonal variation of the settling characteristics in terms of Filament Index (FI) and Sludge Volume Index (SVI) values. M. parvicellas proliferation is favored in Carrousel and oxidation ditches systems especially when primary settling stage was preceeded, whereas its growth is also highly stimulated in intermittent aeration systems, even in the absence of primary settling tanks. Finally there is evidence that Bio-P systems without primary sedimentation inhibit its growth.

Wastewater treatment process impact on energy savings and greenhouse gas emissions

The objective of this research was to assess the energy consumption of wastewater treatment plants (WWTPs), to apply a mathematical model to evaluate their carbon footprint, and to propose energy saving strategies that can be implemented to reduce both energy consumption and greenhouse gas (GHG) emissions in Greece. The survey was focused on 10 WWTPs in Greece with a treatment capacity ranging from 10,000 to 4,000,000 population equivalents (PE). Based on the results, annual specific energy consumption ranged from 15 to 86 kWh/PE. The highest energy consumer in all the WWTPs was aeration, accounting for 40-75% of total energy requirements. The annual GHG emissions varied significantly according to the treatment schemes employed and ranged between 61 and 161 kgCO₂e/PE. The highest values of CO₂emissions were obtained in extended aeration systems and the lowest in conventional activated sludge systems. Key strategies that the wastewater industry could adopt to mitigate GHG emissions are identified and discussed. A case study is presented to demonstrate potential strategies for energy savings and GHG emission reduction. Given the results, it is postulated that the reduction of dissolved oxygen (DO) set points and sludge retention time can provide significant energy savings and decrease GHG emissions.

The role of activated carbon and disinfection on the removal of endocrine disrupting chemicals and non-steroidal anti-inflammatory drugs from wastewater

Endocrine disrupting chemicals and non-steroidal anti-inflammatory drugs are two important groups of emerging pollutants due to their toxicological and chemical characteristics and their persistent detection in the aquatic environment. Wastewater treatment plants are a significant pathway for their transfer to the water courses. It is well evidenced that these chemicals are only partially removed through biological treatment of wastewater and therefore being detected in secondary effluents. This work focuses on the evaluation of the efficiency of two well-established disinfection technologies (chlorination and UV irradiation) along with UV/H 2O 2 and powdered activated carbon (PAC) to remove these chemicals from biologically treated wastewater. Based on the results it is shown that appreciable removal efficiencies due to chlorination should be expected for most of the target compounds, whereas this was not the case for ibuprofen and ketoprofen. With the exemption of diclofenac and ketoprofen direct UV irradiation did not efficiently removed target compounds for UV doses usually applied for disinfection purposes. The application of advanced UV treatment through the addition of H 2O 2 although resulted in increased removal of the target compounds is not sufficient at moderate UV and H 2O 2 doses to achieve satisfactory removal efficiencies. PAC use resulted in sufficient removal of target compounds although high PAC doses were required for some chemicals. Comparison of Freundlich isotherms of this study with those of other studies, derived employing water samples, suggested that the water matrix along with the target compounds concentration range can significantly affect the outcome of the experiments.

Environmental fate of non-steroidal anti-inflammatory drugs in river water/sediment systems

Laboratory tests were conducted with four non-steroidal anti-inflammatory drugs (naproxen, ibuprofen, diclofenac and ketoprofen) under different redox conditions (aerobic, anoxic, anaerobic and sulfate-reducing conditions) in order to assess abiotic and biotic degradation in a river water/sediment system. The river water was sampled from Sperchios River and the sediment was collected from the banks of a rural stream where the discharge point of a wastewater treatment plant is located. To quantitatively describe degradation kinetics of the selected compounds, pseudo first-order kinetics were adopted. According to the results, it can be stated that the concentration of the substances remained constant or decreased only marginally (p≥0.05) in the sterile experiments and this excludes abiotic processes such as hydrolysis or sorption as major removal mechanisms of the target compounds from the water phase and assign their removal to microbial action. Results showed that the removal rate of the compounds decreases as dissolved oxygen concentration in the river water/sediment system decreases. All compounds were found to be biodegradable under aerobic conditions at dissipation half-lives between 1.6 and 20.1days, while dissipation half-lives for naproxen and ketoprofen increase by a factor of 2 under all tested conditions in the absence of oxygen.

Can strict water reuse standards be the drive for the wider implementation of MBR technology

AbstractMembrane bioreactors (MBRs) are currently considered a mature technology for municipal wastewater treatment with many full scale applications worldwide. The drive for the wider implementation of MBR technology can be the increasingly stringent legislation concerning the reuse or discharge of the treated effluent. In this work it is shown that the strict limits recently adopted by Greece concerning reclaimed water reuse can be consistently met when MBR technology and suitable disinfection are applied. MBR permeate met the Greek limit of 5 FC/100 mL for 80% of samples and 50 FC/100 mL for 95% of samples required for unrestricted irrigation when a chlorination dosage of 10 mg min/L was applied and an ultraviolet (UV) radiation dosage of 10 mW s/cm2. On the contrary, secondary effluent from the activated sludge process could not satisfy the given limits even at a chlorination dosage of 600 mg min/L and a UV radiation dosage of 120 mW s/cm2. Tertiary effluent (treated by the activated sludge process an...

Removal of taste and odour from potable water by ozone and Powdered Activated Carbon (PAC).

The paper presents experimental evidence that selection and addition of an appropriate type of Powdered Activated Carbon (PAC) and alternatively or in combination ozonation of the water can be very effective in removal of both geosmin and 2-MIB from surface waters intended for supplying potable water. According to the experimental results, it was shown that the adsorptive capacity of the carbon is about five times greater in the case of geosmin when compared with 2-MIB. Furthermore, addition of ozone at doses in the range 1-3 mg/L for a period of 5-10 min can reduce odour to levels below threshold odour value.