The sludge dewaterability in membrane bioreactors

The influence of the sludge origin on the dewaterability features has been investigated by comparing the experimental results of six membrane bioreactor pilot plants with different configurations. The capillary suction time (CST) and the specific resistance to filtration (SRF), identified as representative of sludge dewaterability features, were measured. The results were related to operational parameters, such as extracellular polymeric substances (EPS) and soluble microbial product (SMP), influent salinity and hydrocarbon, in order to elucidate the influence exerted on the dewaterability. Furthermore, the effect of biofilm and suspended biomass was also investigated. The results showed that during the experimentation carried out with salt and hydrocarbon the sludge dewaterability features significantly worsened (CST above 120 s and SRF above 20 * 1012 m kg-1). Furthermore, the sludge derived from the anoxic reactor resulted as the most affected by EPS and SMP concentration

Assessment of landfill leachate biodegradability and treatability by means of allochthonous and autochthonous biomasses

The biodegradability and treatability of a young (3 years old) municipal landfill leachate was evaluated by means of chemical oxygen demand (COD) fractionation tests, based on respirometric techniques. The tests were performed using two different biomasses: one cultivated from the raw leachate (autochthonous biomass) and the other collected from a conventional municipal wastewater treatment plant after its acclimation to leachate (allochthonous biomass). The long term performances of the two biomasses were also studied. The results demonstrated that the amount of biodegradable COD in the leachate was strictly dependent on the biomass that was used to perform the fractionation tests. Using the autochthonous biomass, the amount of biodegradable organic substrate resulted in approximately 75% of the total COD, whereas it was close to 40% in the case of the allochthonous biomass, indicating the capacity of the autochthonous biomass to degrade a higher amount of organic compounds present in the leachate. The autochthonous biomass was characterized by higher biological activity and heterotrophic active fraction (14% vs 7%), whereas the activity of the allochthonous biomass was significantly affected by inhibitory compounds in the leachate, resulting in a lower respiration rate (SOUR = 13 mg O2 gVSS-1 h-1 vs 37 mg O2 gVSS-1 h-1). The long-term performance of the autochthonous and allochthonous biomasses indicated that the former was more suitable for the treatment of raw landfill leachate, ensuring higher removal performance towards the organic pollutants

Waste activated sludge dewaterability: comparative evaluation of sludge derived from CAS and MBR systems

Sludge dewatering represents, nowadays, one of the greatest operational cost to wastewater treatment cycle. Physical\u2013chemical and biological parameters are recognized to influence the sludge dewaterability. However, many authors agree in identifying the sludge origin as one of the main aspect involved in sludge dewaterability. Indeed, the sludge origin such as the processes involved in liquid\u2013solid separation, seriously affect the sludge features. In order to elucidate the key factors influencing the dewaterability process, the present work is aimed to investigate the influence of the treatment plant lay-out on sludge dewaterability. The analyzed sludge samples were derived from four conventional activated sludge and two membrane bioreactor wastewater treatment plants. Experimental investigation was focused to highlight difference in sludge dewaterability derived from the application of European Standards adopted for sludge characterization. The achieved results confirmed the complexity of the inter-relationships between many factors affecting the sludge dewaterability

Treatment of oily wastewater with membrane bioreactor systems

The aim of the present work was to investigate the behavior of a membrane bioreactor (MBR) system for the treatment of oily wastewater. A bench scale MBR was fed with synthetic wastewater containing diesel fuel. Organic carbon, hydrocarbon and ammonium removal, kinetic constants, extracellular polymeric substances production, and membrane fouling rates were monitored. The MBR plant was operated for more than 200 days, and the results highlighted good carbon removal and nitrification, suggesting a sort of biomass adaptation to hydrocarbons. Membrane fouling analysis showed an increase in total resistance, likely due to hydrocarbons, which caused an irreversible fouling (pore blocking) mainly due to oil deposition

Effect of biomass features on oxygen transfer in conventional activated sludge and membrane bioreactor systems

The aim of the present study was to compare the oxygen transfer efficiency in a conventional activated sludge and a membrane bioreactor system. The oxygen transfer was evaluated by means of the oxygen transfer coefficient (kLa)20 and α-factor calculation, under different total suspended solids concentration, extracellular polymeric substances, sludge apparent viscosity and size of the flocs. The (kLa)20 and α-factor showed an exponential decreasing trend with total suspended solid, with a stronger (kLa)20 dependence in the conventional activated sludge than the membrane bioreactor. It was noted that the (kLa)20 in the conventional activated sludge become comparable to that in membrane bioreactor when the TSS concentration in the conventional activated sludge was higher than 5 gTSS L-1. Operating under high carbon to nitrogen ratio, the (kLa)20 increased in both conventional activated sludge and membrane bioreactor because of the sludge deflocculation and a weaker dependence of (kLa)20 with total suspended solid was noted. The results indicated that the most important parameters on the oxygen transfer efficiency were in order: the total suspended solid concentration, flocs size, sludge apparent viscosity, the protein to polysaccharides ratio and extracellular polymeric substances content. Based on the influence of the main biomass features affecting the (kLa)20 and considering the typical operating conditions in both systems, those of membrane bioreactor appeared to be more favorable to oxygen transfer efficiency compared to conventional activated sludge process

The influence of solid retention time on IFAS-MBR systems: Assessment of nitrous oxide emission

The aim of the present study was to investigate the nitrous oxide (N2O) emissions from a moving bed based Integrated Fixed Film Activated Sludge (IFAS) - membrane bioreactor (MBR) pilot plant, designed according to the University of Cape Town (UCT) layout. The experimental campaign had a duration of 110 days and was characterized by three different sludge retention time (SRT) values (\ue2\u88\u9e, 30 d and 15 d). Results highlighted that N2O concentrations decreased when the biofilm concentrations increased within the aerobic reactor. Results have shown an increase of N2O with the decrease of SRT. Specifically, an increase of N2O-N emission factor occurred with the decrease of the SRT (0.13%, 0.21% and 0.76% of influent nitrogen for SRT = \ue2\u88\u9e, SRT = 30 d and SRT = 15 d, respectively). Moreover, the MBR tank resulted the key emission source (up to 70% of the total N2O emission during SRT = \ue2\u88\u9e period) whereas the highest N2O production occurred in the anoxic reactor. Moreover, N2O concentrations measured in the permeate flow were not negligible, thus highlighting its potential detrimental contribution for the receiving water body. The role of each plant reactor as N2O-N producer/consumer varies with the SRT variation, indeed the aerobic reactor was a N2O consumer at SRT = \ue2\u88\u9e and a producer at SRT = 30 d

An innovative respirometric method to assess the autotrophic active fraction: Application to an alternate oxic-anoxic MBR pilot plant

An innovative respirometric method was applied to evaluate the autotrophic active fraction in an alternate anoxic/oxic membrane bioreactor (MBR) pilot plant. The alternate cycle (AC) produces a complex microbiological environment that allows the development of both autotrophic and heterotrophic species in one reactor. The present study aimed to evaluate autotrophic and heterotrophic active fractions and highlight the effect of different aeration/non aeration ratios in a AC-MBR pilot plant using respirometry. The results outlined that the autotrophic active fraction values were consistent with the nitrification efficiency and FISH analyses, which suggests its usefulness for estimating the nitrifying population. Intermittent aeration did not significantly affect the heterotrophic metabolic activity but significantly affected the autotrophic biomass development. Finally, the heterotrophic active biomass was strongly affected by the wastewater characteristics, whereas the resultant autotrophic biomass was considerably affected by the duration of the aerated phase

Optimization of acetate production from citrus wastewater fermentation

Citrus wastewater is a sugar-rich waste stream suitable for the recovery of energy of material from its treatment. In this study, fermentation of citrus wastewater was carried out to assess the optimal conditions to maximize the bioconversion of the organic substrate into acetate. Unbalanced nutrient (C: N: P 200:0.1:0.1) enabled the highest acetate production. The presence of the particulate organic fraction enabled to obtain a higher acetate concentration regardless the initial COD concentration. Initial pH values higher than 5 did not cause substantial differences on the maximum bioconversion of COD into acetate, whereas pH lower than 5 hindered the hydrolysis process. Lastly, the bioconversion rate of the organic substrate into acetate decreased from a maximum of 23% to a minimum of 8% related to the initial COD. The achieved results demonstrated that the characteristics of citrus wastewater enable its valorisation without the need to apply energy-consuming processes

Sequential batch membrane bio-reactor for wastewater treatment: The effect of increased salinity

In this work, a sequential batch membrane bioreactor pilot plant is investigated to analyze the effect of a gradual increase in salinity on carbon and nutrient removal, membrane fouling and biomass kinetic parameters. The salinity was increased by 2 g NaCl L-1 per week up to 10 g NaCl L-1. The total COD removal efficiency was quite high (93%) throughout the experiment. A gradual biomass acclimation to the salinity level was observed during the experiment, highlighting the good recovery capabilities of the system. Nitrification was also influenced by the increase in salinity, with a slight decrease in nitrification efficiency (the lowest value was obtained at 10 g NaCl L-1 due to lower nitrifier activity). Irreversible cake deposition was the predominant fouling mechanism observed during the experiment. Respirometric tests exhibited a stress effect due to salinity, with a reduction in the respiration rates observed (from 8.85 mgO2 L-1 h-1 to 4 mgO2 L-1 h-1)

Materials recovery from WEEE: current situation in Sicily.

The potential recovery of materials and energy in one year in Italy and in Sicily was estimated assuming that all WEEEs were gathered through the collection – treatment – disposal system implemented according to the rules in force. The embodied energy (EE) recovery associated to material recovery was also estimated, starting from standard values of EE and from yields declared for each component. Mass fractions composition for some categories of WEEE given by a facility in Catania agree with the national averages. Starting from data given by another facility - located in Siracusa - which processes all the five R categories (R1 to R5), potential mass and energy recovery was estimated for this plant. The results compared with national estimates lead to the conclusion that currently this plant contributes by 6% as mass and by 5% for EE recovery. National figures for potential energy recovery from WEEE shows that 10 670 GWh could be theoretically recovered, that is as much as the energy used for civil needs in Italy by two millions people / yr