Foaming control and determination of biokinetic coefficients in membrane bioreactor system under various organic loading rate and sludge retention time

Kinetic coefficients of cell growth and removal of organic substances for modeling Anaerobic-anoxic-aerobic method

Purpose

Anaerobic-anoxic-aerobic process is one of the biological removal processes of nutrients in wastewater treatment. Phosphorus removal by biological method is a new and developed technique that is done by changing the design of suspended growth systems.

Methods

This is a cross-sectional descriptive study, which is a pilot workshop based in the first module, and chemistry, physics and microbiological tests were carried out at the wastewater treatment plant laboratory in one of the cities (Pardis) of Tehran province in 2020-2021 during a period of 12 months. Was completed. In this research, a total of 500 samples were taken from raw wastewater, aeration pond, effluent, secondary sedimentation and return activated sludge.

Results

In this research, the internal decay coefficient and the growth efficiency coefficient are equal to d-1 0.1264 and 0.6579 gVSS/gCOD, respectively. And the maximum specific rate of consumption of food substance and the semi-saturation constant of food substance respectively were gCOD/gVSS.d 3.3467 gCOD/m 25.305. If the specific rate of consumption of food substance or efficiency factor in our research is 0.27 gCOD/gVSS.d and the semi-constant Ks saturation equal to 27.9 gCOD/m has been obtained, this actually shows that the organic matter (COD) in the waste water of Pardis city had a higher degradability (sbCOD).

Conclusion

According to the obtained results, the synthetic coefficients in the Lineweaver-Burk and Hanes models are suitable, but in the Hofstee model, the amount of K and Kd is less than the optimal amount for the proper exploitation of the pilot.

Kinetic Study for Startup of Aerobic Moving Bed Biofilm Reactor in Treatment of Textile Dye Wastewater

Due to high augmentation in population and low availability of land, the quantum of wastewater production has surged resulting in advancements in wastewater treatment systems. To cope under such stressful circumstances, moving bed biofilm reactor (MBBR) proves to be an upgraded treatment technology for industrial and municipal wastewater treatment. The present startup study has been carried out using a laboratory-scale aerobic MBBR with working volume of 25L for textile dye wastewater treatment having AnoxKaldnes K3 media at filling percentage of 50%. In order to acclimatize the microorganisms on textile dye wastewater, the startup of the reactor was carried out using lactose as readily degradable co-substrate with textile dye wastewater in different ratios at hydraulic retention time (HRT) of 24 h. The biofilm on the media was developed in 63 days duration and the reactor attained pseudo-steady state (PSS) in 185 days period. During PSS condition of the MBBR, the maximum chemical oxygen demand (COD) removal efficiency of 92% with mixed liquor suspended solids (MLSS) concentration of 4224 ± 22 mg/L has been achieved. The kinetic study for biodegradation of textile dye wastewater has also been carried out using the Monod growth kinetics. The values of bio-kinetic coefficients of yield of heterotrophic biomass (Y) and endogenous decay coefficient for heterotrophic biomass (Kd) recorded are 0.394 mgVSS/mgCOD.d and 0.087 day-1, respectively. The values of specific substrate removal rate (k), Monod half saturation constant (Ks), and maximum specific growth rate for heterotrophic biomass (µmax) are 0.024 mgCOD/mgVSS.d, 53.203 mg/L, and 0.0095 day-1, respectively, demonstrating the suitability and healthy performance of MBBR for textile dye wastewater treatment.

Biochar Addition in Membrane Bioreactor Enables Membrane Fouling Alleviation and Nitrogen Removal Improvement for Low C/N Municipal Wastewater Treatment

Membrane bioreactors (MBRs) are frequently used to treat municipal wastewater, but membrane fouling is still the main weakness of this technology. Additionally, the low carbon-nitrogen (C/N) ratio influent has been shown to not only increase the membrane fouling, but also introduce challenges to meet the effluent discharge standard for nitrogen removal. Herein, the authors addressed the challenges by adding cost-effective biochar. The results suggested that the biochar addition can enable membrane fouling alleviation and nitrogen removal improvement. The reduced membrane fouling can be ascribed to the biochar adsorption capacity, which facilitates to form bigger flocs with carbon skeleton in biochar as a core. As a result, the biochar addition significantly altered the mixed liquor suspension with soluble microbial product (SMP) concentration reduction of approximately 14%, lower SMP protein/polysaccharide ratio from 0.28 ± 0.02 to 0.22 ± 0.03, smaller SMP molecular weight and bigger sludge particle size from 67.68 ± 6.9 μm to 113.47 ± 4.8 μm. The nitrogen removal is also dramatically improved after biochar addition, which can be due to the initial carbon source release from biochar, and formation of aerobic-anaerobic microstructures. Microbial diversity analysis results suggested more accumulation of denitrification microbes including norank_f__JG30-KF-CM45 and Plasticicumulans. Less relative abundance of Aeromonas after biochar addition suggested less extracellular polymer substance (EPS) secretion and lower membrane fouling rate.

Selection of optimum biological treatment for coking wastewater using analytic hierarchy process

The design of biological treatment process for the coking wastewater (CW) is complicated since wastewater treatment demand is gradually increasing lacking the systematic strategy in efficiency evaluation and advisable selection. Therefore, this study develops a holistic approach by means of the analytic hierarchy process (AHP) that uses numerical representation to rank the preferences of each participating alternatives for evaluation of the advanced biological technologies in CW treatment. Based on survey results, six types reactor combinations were selected as the alternatives, which were further classified as two group according to COD load. The AHP methodology consists of weighting and ranking procedures considering technical, economic, environmental and administration factors defined as criteria layers. Eighteen indicators were chosen as sub-criteria layers. Inclusively beneficial and sustainable biological processes were assessed and ranked along the AHP implementation. The results placed technical indicators to the top position among the criteria layers in the weighting descending order 'technical indicators > economic indicators > environmental indicators > administrative indicators', whereas the weight of indicators in sub-criteria layers fitted in the range of 0.005 to 0.151. The inclusive priority calculation integrating all weight indices of criteria and sub-criteria layers resulted in the anaerobic-anoxic-oxic (A/A/O) combination rising in the hierarchy of the low load group, whereas the oxic-hydrolytic-oxic (O/H/O) process was prioritized in the high load group. The accuracy and objectivity of AHP application was also supported by sensitivity and variability analyses that examines a range for the weights' values and corresponding to alternative scenarios.

Membrane fouling caused by biological foams in a submerged membrane bioreactor: Mechanism insights

Though sludge foaming often occurs and thus causes serious membrane fouling in membrane bioreactors (MBRs), the fouling mechanisms related with the foaming phenomenon have not been well addressed, hindering better understanding and solving foaming problem. In this work, it was interestingly found that, the foulants during the foaming period possessed extremely high specific filtration resistance (SFR) (over 10¹⁶ m kg^-1) and strong adhesion ability to membrane surface. Chemical characterization showed that the proteins (178.57 mg/L) and polysaccharides (209.21 mg/L) in the foaming sample were about 6.4 times and 5.4 times of those in the supernatant sample, suggesting existence of a mechanism permitting continuous production of these foulants in the MBR during the foaming period. It was revealed that the fouling caused by foams was associated with gel layer filtration process, and the extremely high SFR can be interpreted by chemical potential change in the gel filtration process depicted in Flory-Huggins theory. Meanwhile, analyses by the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory showed that the strong adhesion ability stemmed from the high interaction energy between the foaming foulants and membrane surface. In addition, 16S rDNA gene sequencing identified that the abundance of the foaming related bacteria species in the sludge suspension during the foaming period was more than 10 times of that during the non-foaming period. This study offered new mechanism insights into foaming fouling in MBRs.