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Alexander Hendriks

3 records found

Authored

Reconsidering hydrolysis kinetics for anaerobic digestion of waste activated sludge applying cascade reactors with ultra-short residence times

Journal article (2021) - H. Guo, M.J. Oosterkamp, F. Tonin, Alexander Hendriks, Revathy Nair, J.B. van Lier, M.K. de Kreuk

Hydrolysis is considered to be the rate-limiting step in anaerobic digestion of waste activated sludge (WAS). In this study, an innovative 4 stages cascade anaerobic digestion system was researched to (1) comprehensively clarify whether cascading configuration enhances WAS hydrolysis, and to (2) better understand the governing hydrolysis kinetics in this system. The cascade system consisted of three 2.2 L ultra-short solids retention times (SRT) continuous stirred tank reactors (CSTRs) and one 15.4 L CSTR. The cascade system was compared with a reference conventional CSTR digester (22 L) in terms of process performance, hydrolytic enzyme activities and microbial community dynamics under mesophilic conditions (35 °C). The results showed that the cascade system achieved a high and stable total chemical oxygen demand (tCOD) reduction efficiency of 40–42%, even at 12 days total SRT that corresponded to only 1.2 days SRT each in the first three reactors of the cascade. The reference-CSTR converted only 31% tCOD into biogas and suffered process deterioration at the applied low SRTs. Calculated specific hydrolysis rates in the first reactors of the cascade system were significantly higher compared to the reference-CSTR, especially at the lowest applied SRTs. The activities of several hydrolytic enzymes produced in the different stages revealed that protease, cellulase, amino peptidases, and most of the tested glycosyl-hydrolases had significantly higher activities in the first three small digesters of the cascade system, compared to the reference-CSTR. This increase in hydrolytic enzyme production by far exceeded the increase in specific hydrolysis rate, indicating that hydrolysis was limited by solids-surface availability for enzymatic attack. Correspondingly, high relative abundances of hydrolytic-fermentative bacteria and hydrogenotrophic methanogens as well as the presence of syntrophic bacteria were found in the first three digesters of the cascade system. However, in the fourth reactor, acetoclastic methanogens dominated, similarly as in the reference-CSTR. Overall, the results concluded that using multiple CSTRs that are operated at low SRTs in a cascade mode of operation significantly improved the enzymatic hydrolysis rate and extend in anaerobic WAS digestion. Moreover, the governing hydrolysis kinetics in the cascading reactors were far more complex than the generally assumed simplified first-order kinetics.

@en

Mild Thermal Pre-Treatment of Waste Activated Sludge to Increase Loading Capacity, Biogas Production, and Solids’ Degradation: A Pilot-Scale Study

Journal article (2020) - A. Gonzales, H. Guo, Oscar Ortega-Ibáñez, Coert Petri, J.B. van Lier, M.K. de Kreuk, Alexander Hendriks

Sludge pre-treatments are emerging as part of the disposal process of solid by-products of wastewater purification. One of their benefits is the increase in methane production rate and/or yield, along with higher loading capacities of existing digesters. In this study, we report ...

Contributed

Removal of ammonia peaks from effluent wastewater using nitrifying biolm on zeolite

Master thesis (2023) - P. Thiruvenkatachari, M.K. de Kreuk, Sebastiaan Heijman, Alexander Hendriks

Elevated levels of ammonia in discharged water leads to eutrophication and potential toxicity in water bodies. To combat nitrogen pollution, strict ammonium discharge limits of 1 mgNH₄-N/L standard is set by the water framework directory. In many cases, current wastewater treatment facilities struggle to consistently meet this standard, particularly during peak concentration periods. For years now, the influent's peak pattern has been mirrored in the biologically treated water and currently, there lacks an effective solution to address this issue. This study explores use of zeolite in a biological filter, a potential technology to remove ammonia peaks from effluent wastewater. The fundamental concept of this technology involves combining zeolite with a nitrifying biofilm. In this process, the zeolite dampens the ammonia peak by adsorption, while the nitrifying biofilm regenerates the zeolite. Clinoptilolite, a natural zeolite of 1mm particle size and synthetic wastewater were chosen in this study. The impact of competing cations was investigated due to clinoptilolite's affinity for cations. It was found that the presence of other cations decreases ammonium removal capacity by 6.2 times of which potassium is the main competitor. But, percentage of potassium removed is much less than ammonium though it's concentration is 5 times higher. 44.2% of the total potassium was removed in 60 minutes compared to 70.9% ammonium removal. In the experiments with the nitrifying biofilm, it was found, that it does
not affect rate of adsorption by zeolite, but enhances ammonium removal. Experimental results indicate that zeolite can be bio-regenerated effectively, and rate of conversion is faster than rate of desorption of adsorbed ammonium. The system of zeolite and biofilm has some buffer capacity, but cannot compensate for the bicarbonate anions needed for H⁺ released. A BioWin model
was designed to simulate the survival of biomass during extended periods of low concentration, and the results indicated that conversion capacity of the system reduces after 7 days of DWF concentrations. But the biomass can sustain longer periods of DWF concentrations, but it takes some time and exposure to higher substrate concentrations to revive it's capacity. In conclusion this study
confirms the potential in this technology and confirms effective bio-regeneration capabilities. The results from this research can built upon to answer questions regarding knowledge gaps with reactor operation and design. This paves the way for future studies to make it an industrially viable technology.