Explicit oxygen concentration expression for estimating extant biodegradation kinetics from respirometric experiments.

We present a simple method for estimating extant biodegradation kinetic parameters from oxygen uptake data obtained during respirometric experiments. Specifically, a novel closed-form solution based on the Lambert W function is presented for the differential equation describing substrate biodegradation based on the Monod equation. Unlike the existing implicit solution, this novel solution is explicit with respect to the substrate concentration and, when coupled with the oxygen uptake equation, results in a simple algebraic expression for dissolved oxygen concentration in respirometric experiments. This new solution provided highly accurate estimates of dissolved oxygen concentrations with accuracy on the order of 10(-15) for calculations performed using double precision arithmetic. The applicability of this approach for estimating extant biodegradation kinetic parameters was verified using synthetic dissolved oxygen concentration data that incorporated normally distributed noise to mimic experimental data. A combination of the W function description of oxygen concentration and a nonlinear optimization routine resulted in estimates of the Monod kinetic parameters, mu(m) and K(s), that were close to the actual values, indicating the suitability of this approach for extant kinetic parameter estimation. This approach was subsequently tested on experimental oxygen concentration data obtained during ethylene-glycol biodegradation in respirometric experiments. The availability of simple algorithms for evaluating the W function makes the new solution easier to compute than current methods that rely on numerical solution of differential or nonlinear equations. The simplicity and accuracy associated with use of the W function to describe oxygen concentration data should make it an attractive approach for estimating extant Monod biodegradation kinetic parameters from respirometric experiments.

Comparison of temperature-phased and two-phase anaerobic co-digestion of primary sludge and municipal solid waste.

Characterization of the similarities and differences between two-phase and temperature-phased systems treating primary wastewater sludge (PS) and the organic fraction of municipal solid waste (OFMSW) as substrate was performed by comparing the rates of key steps, including hydrolysis and methanogenesis. Aceticlastic methanogenic rates were determined using batch respirometric tests with inocula from operating two-phase and temperature-phased systems. The initial methane production rates ranged from 0.32 to 0.93 mL methane/g volatile solids (VS)h for all systems, with the greatest rates observed from the first stage of the temperature-phased system. Hydrolysis rates were determined from particulate chemical oxygen demand destruction. The first stage of the temperature-phased system had greater specific hydrolysis rates than the first stage of the two-phase system at each operating condition. The temperature-phased system outperformed the two-phase system in terms of methane production and VS destruction when treating a mixed OFMSW-PS stream at OFMSW-to-PS ratios of 0:100, 20:80, and 40:60. When the feed ratios were 60:40 and 80:20 OFMSW-PS, there was no significant difference in the performance of the two systems. The overall methane yield and VS destruction of the temperature-phased system ranged from 0.299 to 0.418 L/g VS fed and 47.5 to 71.6%, respectively. The overall methane yield and VS destruction of the two-phase system ranged from 0.281 to 0.332 L/g VS fed and 39.6 to 69.3%, respectively.

Struvite precipitation potential for nutrient recovery from anaerobically treated wastes.

Geochemical equilibrium speciation modeling was used to determine optimum conditions for precipitation of magnesium ammonium phosphate, or struvite, for the recovery of nutrients from anaerobically digested wastes. Despite a wide range of pH values with the potential to precipitate struvite, the optimum pH was determined to be 9.0. Bench experiments conducted on effluent from an anaerobic sequencing batch reactor (ASBR) treating swine wastes achieved a maximum of 88% ammonia removal at a pH of 9.5 with added magnesium and phosphate to achieve an ammonium: magnesium: phosphate molar ratio of 1:1.25:1. Struvite precipitation was performed on a continuous basis in a pilot-scale ASBR treating swine wastes. Through the addition of supplemental magnesium and phosphate, the ammonia concentration was reduced from 1500 mg/L as nitrogen to less than 10 mg/L. The supenatant from the struvite precipitation clarifier was recycled to the feed of the ASBR without adverse impact, simulating on-farm effluent reuse as flush water.