Olive mill wastewater biological treatment by fungi biomass

Respirometry tests in wastewater treatment: Why and how? A critical review

Respirometry tests are a widely employed method in wastewater treatment field to characterize wastewater streams, assess toxic/inhibitory effects to the biomass, calibrate mathematical models. Respirometry can allow to fractionize the chemical oxygen demand (COD) in biodegradable and inert fractions, but also provide information related to biomass kinetics and stoichiometry through standardized laboratory techniques. Considering the increasing number of emerging contaminants detected in wastewater effluents, such as pharmaceuticals, personal care products and pesticides, respirometry can be a useful tool to promptly assess any toxic or inhibitory effect in wastewater treatment plants (WWTPs) operations. Beside conventional activated sludge (CAS), in recent years respirometric methods have been applied to innovative fields, such as moving-bed bio-reactors (MBBRs), fungi and microalgae, exploiting natural remediation methods. In particular, respirometry application to microalgae, through the so-called photo-respirometry, has been investigated in the latest years in the treatment of high-nutrient loaded streams, allowing resource recovery in biomass form. In this work, respirometric methods are first introduced from a theoretical basis and then critically discussed by considering the experimental apparatus, the available characterization protocols and the fields of application; the most recent literature findings on respirometry are coupled with authors' experience in the field. A comparison between physicochemical methods and respirometry is made, considering common protocols for WWTP modelling and calibration. The future research needed on the topic is finally outlined, including the coupling of respirometry with microbial community analysis, potentially leading to an enhanced process understanding, an extended respirometry utilization to get specific kinetic and stoichiometric parameters for modelling purposes, and a wider respirometry application as diagnosis tool in WWTP operations.

Respirometric techniques coupled with laboratory-scale tests for kinetic and stoichiometric characterisation of fungal and bacterial tannin-degrading biofilms

In environmental biotechnology applications for wastewater treatment, bacterial-based bioprocesses are mostly implemented; on the contrary, the application of fungal-based bioprocesses, is still challenging under non-sterile conditions. In a previous laboratory-scale study, we showed that when specific tannins are used as the sole carbon source, fungi can play a key role in the microbial community, under non-sterile conditions and in the long term. In a previous study, an engineered ecosystem, based on fungal tannin biodegradation, was successfully tested in a laboratory-scale bioreactor under non-sterile conditions. In the present study, a kinetic and stoichiometric characterisation of the biomass developed therein was performed through the application of respirometric techniques applied to the biomass collected from the above-mentioned reactor. To this aim, a respirometric set-up was specifically adapted to obtain valuable information from tannin-degrading fungal biofilms. A mathematical model was also developed and applied to describe both the respirometric profiles and the experimental data collected from the laboratory-scale tests performed in the bioreactor. The microbial growth was described through a Monod-type kinetic equation as a first approach. Substrate inhibition, decay rate and tannin hydrolysis process were included to better describe the behaviour of immobilised biomass selected in the tannin-degrading bioreactor. The model was implemented in AQUASIM using the specific tool Biofilm Compartment to simulate the attached fungal biofilm. Biofilm features and transport parameters were either measured or assumed from the literature. Key kinetic and stoichiometric unknown parameters were successfully estimated, overcoming critical steps for scaling-up a novel fungal-based technology for tannins biodegradation.

Comparative evaluation of the microbial community in biological processes treating industrial and domestic wastewaters

AIMS

Comparison of the microbial composition and process performance between laboratory scale processes treating domestic and vegetable oil wastewaters.

METHODS AND RESULTS

Two laboratory scale modified Ludzack-Ettinger processes were operated under similar operating conditions. One process was fed domestic wastewater and the other an industrial wastewater, vegetable oil effluent. Nitrogen removal capacities of the processes were similar. The industrial process exhibited a lower COD removal capacity and oxygen utilization rate, although a greater mixed liquor volatile suspended solids concentration was observed in the industrial process. Fluorescent in situ hybridization (FISH) with probes EUBmix, ALF1b, BET42a, GAM42a and HGC69a revealed that 81% and 72% of total cells stained with 4', 6-diamidino-2-phenylindole (DAPI) within the domestic and industrial processes respectively bound to EUBmix. This indicated a slightly lower Eubacterial population within the industrial process. The alpha-proteobacteria was the dominant community in the industrial process (31% of EUBmix), while the beta-proteobacteria dominated the domestic process (33% of EUBmix).

CONCLUSIONS

The findings served to establish a difference in the microbial population between the processes. Therefore, the class alpha-proteobacteria could play a primary role in the degradation of vegetable oil effluent.

SIGNIFICANCE AND IMPACT OF THE STUDY

This research will aid in process design and retrofitting of biological processes treating vegetable oil effluent.