Evaluation of biomass activity and wastewater characterization in a UCT-MBR pilot plant by means of respirometric techniques
Research Highlights
►Operational conditions and SRT strongly influence the biomass activity. ►Decrease of heterotrophic activity when operating with complete sludge retention. ►Good development of nitrifying bacteria to the detriment of heterotrophic one. ►Respirometry is a suitable tools for UCT-MBR biomass characterisation.
Introduction
Nowadays, due to the increasing awareness about environmental impact of pollutant discharges, the effluent standards are becoming more and more stringent, leading to increased requirements for Wastewater Treatment Plant (WWTP). In this context, the technical and scientific community in the last years showed a growing interest in developing innovative technologies that, together with very high removal efficiencies, can lead to a very low space and volume request. A possible solution to cope with such issues is represented by membrane bioreactors (MBRs), which are combined systems including a bioreactor and a filtration unit (usually an ultrafiltration or microfiltration membrane). More specifically, such systems compared to the traditional ones, like the conventional activated sludge (CAS) processes, which require large aeration and settling tanks, have shown higher efficiency in terms of effluent concentrations as well as smaller footprint and sludge production, due to higher biomass concentration in the bioreactor [1]. Further, MBRs enable high treatment levels in terms of effluent total suspended solid (TSS) concentrations, organic matter and total nitrogen (TN). More in detail, the very high biomass concentration, compared to the available food in the system, contributes to create an environment where bacteria are facing starvation condition so they are not in a physiological state for cell growth [2]. On the other hand, the high sludge retention times (SRTs), typical of MBR system, are highly advantageous for the growth of nitrifying bacteria [1]. Concerning nutrient removal, Ramphao et al. (2005) discussed about the influence of the MBR solid separation on the design of biological nutrient removal (BNR) systems which result smaller than the equivalent conventional systems [3]. On the other hand, Durante et al. and Parco et al. [4], [5] have focused the attention on the influence of the size of the MBR flocs on substrates diffusive transport. However, up to now, the knowledge concerning the influence that high solid concentrations in the mixed liquor as well as the nature of the selected biomass have on the BNR process is controversial and still limited. Indeed, in such systems, a modification in the biomass biokinetic behaviour can arise, compared to that of a CAS process. In this context, respirometric techniques [6] should represent a useful tool for the characterization of the biokinetic behaviour of bacteria in a MBR process, to insert in mathematical models in the design phase, as well as to monitor the biomass viability [7], [8]. Indeed, oxygen uptake rate (OUR), i.e. the oxygen consumption per unit volume per unit time, is widely recognized as an important parameter in order to monitor the biomass viability [9]. On the other hand, in the case of domestic wastewaters with contributions of industrial wastewater, and in a process operated with high SRTs, it might be of paramount interest the respirometric procedures in order to better characterise wastewater and biomass viability.
Bearing in mind such considerations, the paper presents some results of a study aimed at evaluating the heterotrophic and autotrophic kinetic parameters, in terms of organic and nitrogen removal, as well as wastewater chemical oxygen demand (COD) fractionation in a UCT-MBR pilot plant using respirometric techniques.
Section snippets
Pilot plant and operating conditions description
The experimental investigations were carried out on a MBR pilot plant, conceived for nutrient removal, built at the Acqua dei Corsari (Palermo) WWTP. In Fig. 1, the pilot plant layout is reported.
The pilot plant scheme was an adaptation of the UCT process [10] with a final membrane filtration unit instead of the conventional secondary clarifier. It consisted of three reactors in series, anaerobic (mean volume 71.6 l), anoxic (mean volume 164.9 l) and aerobic (mean volume 327 l) respectively,
Pilot plant performances
As previously discussed, during the investigated period the average MLSS concentrations for the pilot-scale MBR ranged from 3 to 6.5 g/l and the average percentage of volatile fraction was almost equal to 70%. The observed yield coefficient (Yobs) was near to 0.07 gVSSgCODox−1, after steady-state conditions were reached (day 76th), in good agreement with results obtained in previous experimental studies on MBR plants [16].
During the experimental period, the pilot plant reduced the average
Conclusions
An experimental gathering campaign on a UCT-MBR pilot plant, conceived for biological nutrient removal, was performed. One of the main aims of the study was the evaluation of the kinetic parameters of both heterotrophic and autotrophic biomass, as well as the COD fractionation, with the aid of respirometric batch tests. The experimental observations highlighted a decrease in the kinetic parameters for heterotrophic bacteria compared to that of a CAS system, even if they increased when the pilot
References (32)
- et al.
Aerobic domestic waste water treatment in a pilot plant with complete sludge retention by cross-flow filtration
Water Res.
(1995) - et al.
Uncertainty assessment of a membrane bioreactor model using the GLUE methodology
Biochem. Eng. J.
(2010) - et al.
An integrated model for physical-biological wastewater organic removal in a submerged membrane bioreactor: model development and parameter estimation
J. Membr. Sci.
(2008) - et al.
Respirometry in control of the activated sludge process
Water Sci. Technol.
(1996) - et al.
Estimating biomass yield coefficients for autotrophic ammonia and nitrite oxidation from batch respirograms
Water Res.
(2001) - et al.
A new method for the assessment of heterotrophic endogenous respiration rate under aerobic and anoxic conditions
Water Sci. Technol.
(1998) - et al.
Zero net growth in a membrane bioreactor with complete sludge retention
Water Res.
(2005) - et al.
Enhanced biological nutrient removal using MUCT–MBR system
Bioresour. Technol.
(2009) - et al.
Estimating (combination of) Activated Sludge Model No.1 parameters and component by respirometry
Water Sci. Technol.
(1999) - et al.
Characterization of tannery wastewater and biomass in a membrane bioreactor using respirometric analysis
Bioresour. Technol.
(2008)
A modified Activated Sludge Model to estimate solids production at low and high solids retention time
Water Res.
A model for membrane bioreactor process based on the concept of formation and degradation of soluble microbial products
Water Res.
A unified theory for extracellular polymeric substances, soluble microbial products, and active and inert biomass
Water Res.
Steady-state modelling of bio-fouling potentials with respect to the biological kinetics in the submerged membrane bioreactor (SMBR)
J. Membr. Sci.
Kinetic interpretation of nitrogen removal in pilot scale experiments
Water Res.
Nitrification and mass balance with a membrane bioreactor for municipal wastewater treatment
Water Sci. Technol.
Cited by (56)
Influence of bisphenol A occurrence in wastewaters on biomass characteristics and activated sludge process performance
2021, Science of the Total EnvironmentCitation Excerpt :BPA detection was achieved at wavelength of 214 nm and a retention time of 2.3 min.BPA limit detection was 0.01 mg·L−1. Respirometric techniques provide valuable information of biomass activity (Bina et al., 2018; Di Trapani et al., 2011). The rate at which microorganisms consume oxygen in the substrate biodegradation process is related to biomass activity.
Recent progress in integrated fixed-film activated sludge process for wastewater treatment: A review
2020, Journal of Environmental ManagementDetermination and evaluation of kinetic parameters of activated sludge biomass from a sludge reduction system treating real sewage by respirometry testing
2019, Journal of Environmental ManagementEffect of a co-substrate supply in a MBR treating shipboard slop: Analysis of hydrocarbon removal, biomass activity and membrane fouling tendency
2018, Biochemical Engineering Journal