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Thursday, October 20, 2011

Stability and inhibition of anaerobic processes caused by insufficiency or excess of ammonia nitrogen


DOI: 10.1007/s00253-011-3625-4 (2011)

Abstract



Ammonia increases buffer capacity of methanogenic medium in mesophilic anaerobic reactor thus increasing the stability of anaerobic digestion process. Optimal
ammonia concentration ensures sufficient buffer capacity
while not inhibiting the process. It was found out in this
paper that this optimum depends on the quality of anaerobic
sludge under investigation. The optimal concentrations for
methanogens were 2.1, 2.6 and 3.1 g/L of ammonia
nitrogen in dependence on inoculum origin. High ammonia
nitrogen concentration (4.0 g/L) inhibited methane production, while low ammonia nitrogen concentration (0.5 g/L)
caused low methane yield, loss of biomass (as VSS) and
loss of the aceticlastic methanogenic activity. It was found
out that negative effect of low ammonia nitrogen concentration on biomass is caused not only by low buffer
capacity but also by insufficiency of nitrogen as nutrient.
It was also found out that anaerobic sludge with higher
ammonia nitrogen concentration (4.2 g/L) tolerates even
concentration of volatile fatty acids (160 mmol/L) which
causes inhibition of the process with low ammonia nitrogen
concentration (0.2 g/L).

Tuesday, October 18, 2011

Comparative influential effects of mass transfer resistance in acetate-fed and glucose-fed sequential aerobic sludge blanket reactors

Chemical Engineering Journal
Volume 174, Issue 1, 15 October 2011, Pages 182-189

Hsin-Hsien Chou, Ju-Sheng Huang , Chun-Wen Tsao, Yen-Chun Lu

Abstract



A laboratory study was undertaken to explore the influential effects of mass transfer resistance on overall substrate removal in acetate-fed and glucose-fed sequential aerobic sludge blanket reactors. In both reactors, solids retention time decreased with increasing OLR [2–8 kg chemical oxygen demand (COD)/m3 d], resulting in increasing specific substrate utilization rates. The obtained kinetic parameters values (k/Ks ratio) indicated that the microbial reaction rate for acetate was higher than that for glucose. The simulated mass transfer parameter values (ϕ2, Bi, L, and η) and substrate concentration profiles in the granule indicated that the overall substrate removal in the acetate-fed and glucose-fed reactors are intra-granular diffusion controlled, and the influential effect of intra-granular mass transfer resistance in the glucose-fed reactor is relatively greater. The simulated results also disclosed that the optimaldp for acetate-fed and glucose-fed reactors should be no greater than 3.5 and 2.5 mm, respectively. The validated kinetic model and the obtained kinetic parameter values can be appropriately used to simulate treatment performance of the SASB reactors treating simple substrates.

Highlights

► A laboratory study was undertaken to explore the influential effect of mass transfer resistance on overall substrate removal in acetate-fed and glucose-fed sequential aerobic sludge blanket (SASB) reactors. ► The size of acetate-fed granules was smaller than that of glucose-fed granules while the biomass density of the former was slightly higher than that of the latter. The obtained kinetic parameters (k/Ks ratios) indicated that the microbial reaction rate for acetate was higher than that for glucose. ► The calculated COD removal efficiencies using the kinetic model (incorporating intrinsic kinetics) agreed well with the experimental results, implying that the proposed model can properly describe the overall substrate removal rate in the SASB reactor. ► By applying the validated kinetic model, the simulated mass transfer parameter values (ϕ2, Bi, L, and η) and substrate concentration profiles in the granule indicated that the overall substrate removal in the acetate-fed and glucose-fed reactors are evidently intra-granular diffusion controlled, and the influential effect of glucose-fed granules is greater than acetate-fed granules. ► The simulated results disclosed that the optimal granular sizes for acetate-fed and glucose-fed reactors should be no greater than 3.5 and 2.0–2.5 mm, respectively.


Sunday, February 20, 2011

Calcium augmentation for enhanced denitrifying granulation in sequencing batch reactors

Bioprocess Chemistry (2011)-doi:10.1016/j.procbio.2011.01.016 

Ya-Juan Liu and Darren Delai Sun

Abstract



Abstract

This study investigated calcium augmentation for enhanced denitrifying granulation in sequencing batch reactors (SBRs) supplemented with different calcium concentrations of 0, 50 and 100 mg Ca2+ l−1, respectively. Results showed that high calcium concentration would favor the formation of big and fast-settling denitrifying granules. Extracellular proteins (PN) were found to increase, whereas extracellular polysaccharides (PS) almost remained unchanged with granulation in all three SBRs. Moreover, the PN contents in mature denitrifying granules were positively related to feed calcium concentration. These suggested that PN would play a more important role than PS in denitrifying granulation process. It was also revealed that about 2.5–2.9% of calcium in denitrifying granules was bound with extracellular polymeric substances (EPS), and further helped to strengthen the structure of denitrifying granules. Mature denitrifying granules cultured with 50 mg Ca2+ l−1 exhibited the highest specific denitrification rate (DNR) of 1040 mg N g−1 VSS d−1.
Keywords: Denitrifying granulation; Calcium; Sequencing batch reactors; Extracellular polymeric substances; Extracellular proteins; Specific denitrification rate

Tuesday, January 25, 2011

An energy evaluation of coupling nutrient removal from wastewater with algal biomass production

Applied Energy (2011) - doi:10.1016/j.apenergy.2010.12.056
Belinda S.M. Sturm,  Stacey L. Lamer

Abstract

Recently, several life cycle analyses of algal biodiesel from virtual production facilities have outlined the potential environmental benefits and energetic balance of the process. There are a wide range of assumptions that have been utilized for these calculations, including the addition of fertilizers and carbon dioxide to achieve high algal yields in open ponds. This paper presents an energy balance of microalgal production in open ponds coupled with nutrient removal from wastewater. Actual microalgal yields and nutrient removal rates were obtained from four pilot-scale reactors (2500 gallons each) fed with wastewater effluent from a conventional activated sludge process for 6 months, and the data was used to estimate an energy balance for treating the total average 12 million gallons per day processed by the wastewater treatment plant. Since one of the most energy-intensive steps is the dewatering of algal cultures, several thickening and dewatering processes were compared. This analysis also includes the energy offset from removing nutrients with algal reactors rather than the biological nutrient removal processes typically utilized in municipal wastewater treatment. The results show that biofuel production is energetically favorable for open pond reactors utilizing wastewater as a nutrient source, even without an energy credit for nutrient removal. The energy content of algal biomass was also considered as an alternate to lipid extraction and biodiesel production. Direct combustion of algal biomass may be a more viable energy source than biofuel production, especially when the lipid content of dry biomass (10% in this field experiment) is lower than the high values reported in lab-scale reactors (50–60%).
Keywords: Algal biofuel; Nutrient removal; Wastewater treatment; Energy balance; Dewatering