Evaluation of biomass activity in membrane bioreactors by means of respirometric techniques

The paper reports the main results of a respirometric experimental survey carried out on several membrane bioreactor pilot plants, characterized by different pilot plant layouts as well as operational conditions. The main aim was to assess the influence of specific conditions on biokinetic/stoichiometric parameters. In particular, the respirometric tests were specifically aimed at investigating the activity of both heterotrophic and autotrophic bacterial species. The achieved results showed that the plant configuration and the features of the feeding wastewater and operational conditions determine significant variation of the kinetic coefficients. The respirometric analysis was confirmed to be a simple and effective tool for the evaluation of the actual biomass kinetic parameters, to be used in mathematical models for the design phase as well as for monitoring the biomass viability during plant operations

Mathematical modelling of biogas from municipal solid waste landfil

Sanitary landfills for municipal solid wastes can be considered as large biological reactors where the organic fraction of municipal solid waste undergoes anaerobic digestion producing gas and liquid emissions. Leachate production from municipal sanitary landfills is currently recognized as a major environmental burden associated with municipal solid waste management and it may be responsible for local pollution of groundwater and soil. Moreover, the fate of the organic compounds within the landfill body is of primary importance since it directly influences the production of landfill gas. The aim of the paper is to propose an integrated mathematical model able to simulate, on one hand, the vertical leachate fluxes throughout a municipal solid waste landfill (considering the fate of both inorganic and organic contaminants within the landfill leachate pathway), while, on the other hand, the production of landfill gas by means of two different approaches. In detail, the mathematical model was based on mass balance equations and was composed by two sub-models: one for the simulation of moisture distribution, whilst the other one for the simulation of the organic/inorganic contaminant concentrations. The simulation of landfill gas production was based on two different approaches. The integrated model has been applied to a real landfill considered as a case study, the landfill of Pescantina (Italy), with the landfill body divided into N horizontal layers. The results confirmed that the proposed integrated model can be a useful tool for the landfill operator in order to analyze the physical, chemical and biological phenomena occurring within the landfill body

TREATMENT OF LANDFILL LEACHATE IN SBR SYSTEMS: ANALYSIS OF BIOMASS ACTIVITY BY MEANS OF RESPIROMETRIC TECHNIQUES

In the last decades landfilling has been the main method of municipal solid waste (MSW) disposal in many countries. MSW landfills are usually considered as a large biological reactor where the MSWs undergo anaerobic digestion producing gas and liquid emissions. Aged, or mature leachate, which is produced by older landfills, can be very refractory; for this reason mature leachate is difficult to treat alone, but it can be co-treated with sewage or domestic wastewater. The aim of the study was to investigate the feasibility of co-treatment of landfill leachate and synthetic wastewater in different percentages, in terms of process performance and biomass activity, by means of respirometric techniques. Two sequencing batch reactors (SBR) were fed with synthetic wastewater and different percentages of landfill leachate (respectively 10% and 50% V/V in SBR1 and SBR2). The obtained results showed a good organic carbon removal efficiency for both reactors; ammonia removal efficiency showed different trends between SBR1 and SBR2, probably due to inhibition factors exerted by high landfill leachate percentage present in SBR2

Towards a conceptual mathematical tool linking physical and biological processes for a reduction of ghg emissions from an mb-mbr plant

The current study explores the influence of the air flow rate on greenhouse gas (GHG) emissions (direct and indirect), the operational costs (OCs), the effluent quality index (EQI) and effluent fines (EF). An University Cape Town (UCT) moving bed (MB) membrane bioreactor (MBR) pilot plant has been considered as case study where the influence of the air flow rate on the biological and physical processes has been analyzed. Constitutive relationships between the air flow rate and some performance indicators (i.e., EQI, OCs, direct and indirect GHG emissions) have been identified. Results showed that the EQI increases at low flow rate likely due to the dissolved oxygen (DO) limitation in the biological processes. Direct GHGs are influenced by air flow exponentially increasing with the increase of the air flow due to the anoxic N2O contribution. Irreversible membrane fouling reduce from 98% to 85% with the increasing of the air flow rate from 0.57 m3 h-1 to 2.56 m3 h- 1. However, the increase of the air flow rate leads to the increase of the N2O-N flux emitted from the MBR (from 40% to 80%). In order to establish a mathematical tool to reduce GHG emissions maintaining good effluent quality, results suggest of adopting a relationship based on a “multiple objective”

Nitrous oxide emission from a moving bed membrane biofilm reactor: the effect of the sludge retention time

The aim of the present study was to investigate the nitrous oxide (N2O) emissions from a University of Cape Town (UCT) moving bed membrane bioreactor pilot plant. An experimental campaign was carried out during 60 days with three different sludge retention time (SRT). The pilot plant reactor was provided of funnel shape covers that guaranteed gas accumulation in the headspace. The results highlighted that N2O concentrations significantly increased when the biofilm concentrations increased within the aerobic and anoxic compartments. Furthermore, results have shown an increase of N2O with the decrease of SRT. Moreover, the MBR tank resulted the key emission source (up to 70% of the total N2O emission during SRT=∞ 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

Carbon and nutrient biological removal in a University of Cape Town membrane bioreactor: Analysis of a pilot plant operated under two different C/N ratios

The effect of the carbon-to-nitrogen (C/N) ratio variation in a University of Cape Town Membrane bioreactor (UCT-MBR) was investigated. The experimental campaign was divided into two phases, each characterized by a different C/N ratio (namely, 10 and 5, Phase I and Phase II, respectively). The UCT-MBR pilot plant was analysed in terms of carbon and nutrients removal, biomass respiratory activity, activated sludge features and membrane fouling. The results highlighted that the nutrients removal was significantly affected by the decrease of the C/N ratio during the Phase II. The biological carbon removal was also affected by the low C/N value during the Phase II. Indeed, the average biological COD removal efficiency was equal to 72.9% during the Phase II, while the average value was 82.8% in the Phase I. The respirometric batch test suggested that both heterotrophic and autotrophic species were severely affected by the lower C/N ratio in the Phase II. Moreover, a decrease of the membrane filtration properties was observed during the Phase II, mainly due to the worsening of the activated sludge features, which enhanced the increase of SMP production

LE EMISSIONI DI GAS CLIMALTERANTI DAI SISTEMI MBR

La salvaguardia dell’ambiente pone ad oggi delle nuove sfide nei confronti dei cambiamenti climatici. Invero, il fenomeno del climate change, i cui principali effetti portano ad un innalzamento delle temperature a seguito del rilascio di emissioni di gas climalteranti (i.e., anidride carbonica, CO2; metano, CH4; protossido di azoto, N2O), richiede degli interventi a breve, medio e lungo termine per limitare i sempre più crescenti danni ambientali. Gli impianti di depurazione contribuiscono anch’essi al fenomeno del climate change attraverso le emissioni di gas climalteranti (Global Water Research Coalition – GWRC, 2011; Law et al., 2012; Zhan et al., 2017)

Removal of carbon and nutrients from wastewater in a moving bed membrane biofilm reactor: the influence of the sludge retention time

A University of Cape Town (UCT) pilot plant combining both membrane bioreactor (MBR) and moving bed biofilm reactor (MBBR) technology was monitored. Three experimental Phases were carried out by varying the mixed liquor sludge retention time (SRT) (indefinite, 30 and 15 days, respectively). The system performance has been investigated during experiments in terms of: organic carbon, nitrogen and phosphorus removal, biokinetic/stoichiometric constants, membrane fouling tendency and sludge dewaterability. The observed results showed that by decreasing the SRT the UCT pilot plant was able to maintain very high total COD removal efficiencies, whilst the biological COD removal efficiency showed a slight decrease. Nitrification was only slightly affected by the decrease of the mixed liquor SRT, showing high performance (as average). This result could be related to the presence of the biofilm able to sustain nitrification throughout experiments. Conversely, the average P removal efficiency was quite moderate, likely due to the increase of the ammonium loading rate that could promote an increased NO3-N recycled from the anoxic to the anaerobic tank, interfering with phosphorus accumulating organisms (PAOs) activity inside the anaerobic tank. Membrane fouling increased at 30 days SRT likely due to a reduction of protective cake pre-filter effect. Moreover, it was noticed the increase of the resistance due to pore blocking and a general worsening of the membrane filtration properties

Interlinkages between operational conditions and direct and indirect greenhouse gas emissions in a moving bed membrane biofilm reactor

Nitrous oxide (N2O) can be emitted during wastewater treatment contributing to the global warming due to its high global warming potential,. During the last ten years, several efforts have been provided to improve knowledge on: key mechanisms, operating factors and influent features affecting the N2O production/emission. However, the knowledge on the investigated issues is not completely mature. Indeed, in terms of mathematical modelling, literature shows that a reliable model has not yet been established due to the huge data set required and the complexity of the mechanistic models indicated as the most accurate. In this work, the first attempt to perform a multiregression analysis is presented with the final aim to get a simple and easy tool for N2O estimation from wastewater treatment plant. The multiregression analysis has been performed by testing both simple and complex equations by means of Monte Carlo simulations. Data acquired from an University Cape Town moving bed membrane bioreactor pilot plant have been adopted. The pilot plant has been operated at different sludge retention times. Results of the simple linear regression analysis show that such approaches are suitable to predict N2O flux emitted from each tank of the plant and dissolved in the permeate. For some tested cases, a high efficiency (obtained comparing simulated and measured data) was obtained (e.g., 0.96 for N2O-N dissolved in the effluent). The results show that the dependence with the available measured data changes with the operational conditions. Conversely, results related to the complex multiregression analysis reveal that no unique equation valid for different operational conditions can be established