Model-based investigation of the chemical phosphorus removal potential of the peroxide regenerated iron-sulfide control technology.

In this study, the potential of using peroxide regenerated iron-sulfide control (PRI-SC®) for chemical phosphorus removal utilizing the existing iron sulfide found in wastewaters was investigated in batch tests and compared in full-scale facility-wide simulations to using iron salts. PRI-SC is a combination treatment that utilizes iron salts and hydrogen peroxide in a synergetic fashion, where hydrogen peroxide is used in regenerating the spent iron salt in situ in the form of iron sulfide, yielding ferric iron and colloidal sulfur. A simplified kinetic model was developed, calibrated, and integrated into a facility-wide model to simulate the process at the full-scale. Experimental results showed that dosing hydrogen peroxide, even at doses lower than the stoichiometrically required to oxidize iron sulfide, freed, and oxidized sulfide bound ferrous iron to ferric iron, which was consequently hydrolyzed and affected phosphorus removal. Higher dosing of hydrogen peroxide did not affect change in the speciation of sulfur remaining predominantly as elemental sulfur. Simulations showed that the application of PRI-SC with supplemental ferric iron dosing was able to cut the costs of chemicals addition up to 53% while maintaining a steady-state effluent phosphate concentration below 0.01 mg/L. PRACTITIONER POINTS: The kinetic model was used to optimize ferric iron and hydrogen peroxide dosing. The developed model can be integrated in existing wastewater process simulators. Dosing hydrogen peroxide effectively oxidized ferrous iron to ferric iron. The combination of hydrogen peroxide and iron salts can reduce the chemical addition cost by 53%.

Biological nutrient removal enhancement using fermented primary and rotating belt filter biosolids.

This research compared the impact of two primary treatment options (i.e. primary clarification and rotating belt filtration (RBF)) on biological nutrients removal (BNR) process, using sludge fermentation liquid (SFL) as a carbon source. The liquid fraction of both fermented primary and RBF sludges comparably enhanced BNR. Despite the significant contribution of the unpurified SFL to the sharp increase in nutrient levels; i.e. 47%-64% (primary effluent; PE), and 45%-53% (RBF) of the soluble nitrogen and phosphorus loads; readily biodegradable COD and volatile fatty acids (VFAs) fractions of the combined feed increased significantly (2.5-6.1 times), compared to the original feed by additional SFL. Removal efficiencies in the reactors reached 57% (total nitrogen) and 92% (total phosphorus) after addition of SFL. Effluent nitrogen and phosphorus of the two reactors were close in the range of 15 ± 6 mg N/L, and 0.5 ± 0.3 mg P/L, respectively. Kinetics studies showed denitrification rates of 1.3, and 1.13 kg NO3-N/m3.d for primary effluent and RBF effluent-fed reactors, respectively. Phosphorus release rates were 11.7 and 9.7 mg PO4-P/g VSS.h, for primary, and RBF effluents, respectively; showing 20%-22% lower rates in the RBF SFL. Incorporating experimental data into a plant-wide model for a 100 MLD facility receiving typical medium strength wastewater, showed that although primary treatment enhanced the biogas production by 96% (primary clarification) and 62% (RBF) trains; combined fermentation and anaerobic digestion was effective to enhance the biogas production by 59% on average, compared to the base scenario without primary treatment. Additionally, if primary clarification exists, then the addition of fermentation results in additional revenue of C$1890/d in the plant, considering additional revenue of C$2230/d due to VFA generation in contrast to only C$340/d loss due to the reduced methane production.

Hydrogen production from sugar beet juice using an integrated biohydrogen process of dark fermentation and microbial electrolysis cell.

An integrated dark fermentation and microbial electrochemical cell (MEC) process was evaluated for hydrogen production from sugar beet juice. Different substrate to inoculum (S/X) ratios were tested for dark fermentation, and the maximum hydrogen yield was 13% of initial COD at the S/X ratio of 2 and 4 for dark fermentation. Hydrogen yield was 12% of initial COD in the MEC using fermentation liquid end products as substrate, and butyrate only accumulated in the MEC. The overall hydrogen production from the integrated biohydrogen process was 25% of initial COD (equivalent to 6 mol H2/mol hexoseadded), and the energy recovery from sugar beet juice was 57% using the combined biohydrogen.

Treatment of thin stillage in a high-rate anaerobic fluidized bed bioreactor (AFBR).

The primary objective of this work was to investigate the treatability of thin stillage as a by-product of bioethanol production plants using an anaerobic fluidized bed bioreactor (AFBR) employing zeolite with average diameter of (d(m)) of 425-610 µm and specific surface area (SSA) of 26.5m(2)/g as the carrier media. Despite the very high strength of thin stillage with chemical oxygen demand of 130,000 mg TCOD/L and suspended solids of 47,000 mg TSS/L, the AFBR showed up to 88% TCOD and 78% TSS removal at very high organic and solids loading rates (OLR and SLR) of 29 kg COD/m(3)d and 10.5 kg TSS/m(3)d respectively and hydraulic retention time (HRT) of 3.5 days. Methane production rates of up to 160 L/d at the steady state equivalent to 40 L(CH4)/L(thin stillage)d and biogas production rate per reactor volume of 15.8L(gas)/L(reactor)d were achieved.

Comparative assessment of single-stage and two-stage anaerobic digestion for the treatment of thin stillage.

A comparative evaluation of single-stage and two-stage anaerobic digestion processes for biomethane and biohydrogen production using thin stillage was performed to assess the impact of separating the acidogenic and methanogenic stages on anaerobic digestion. Thin stillage, the main by-product from ethanol production, was characterized by high total chemical oxygen demand (TCOD) of 122 g/L and total volatile fatty acids (TVFAs) of 12 g/L. A maximum methane yield of 0.33 L CH(4)/gCOD(added) (STP) was achieved in the two-stage process while a single-stage process achieved a maximum yield of only 0.26 L CH(4)/gCOD(added) (STP). The separation of acidification stage increased the TVFAs to TCOD ratio from 10% in the raw thin stillage to 54% due to the conversion of carbohydrates into hydrogen and VFAs. Comparison of the two processes based on energy outcome revealed that an increase of 18.5% in the total energy yield was achieved using two-stage anaerobic digestion.