Process control and design considerations for methanol-induced denitrification in a sequencing batch reactor.

The primary goal of this research was to determine the effect of methanol-induced denitrification on volatile suspended solids production, settleability, and oxidation-reduction potential in a full-scale sequencing batch reactor. Batch tests were also conducted to determine the influence of mixing and acclimatization on the denitrification of wastewater with methanol. The observed sludge production in the full-scale sequencing batch reactor with methanol addition was 0.21 kg volatile suspended solids l(-1) methanol, versus the calculated stoichiometric sludge production of 0.17 kg volatile suspended solids l(-1) methanol. The settleability in the full-scale sequencing batch reactor, measured by the sludge volume index, increases linearly with increasing denitrification rate. The total change in the oxidation-reduction potential magnitude during a sequencing batch reactor cycle increased linearly with increasing denitrification rate. A minimum of 55% increase in the denitrification rate was observed in a batch reactor with methanol addition and a sludge acclimatized to methanol addition, compared to a batch reactor with methanol addition and a non-acclimatized sludge. The non-acclimatized batch reactor had a negligible denitrification rate without methanol addition. However, significant denitrification rates were observed in the acclimatized batch reactors without methanol addition, potentially caused by microbial storage or an increased population of denitrifiers that scavenge any available carbon. A completely mixed batch reactor, with sludge acclimatized to methanol addition during the anoxic cycle, had an increase in the denitrification rate ranging from 660%, without methanol addition, to 200%, with a methanol dosage of 12.7 mg l(-1), compared to the unmixed batch reactor with an acclimatized sludge. Therefore, mixing appears to be critical to the denitrification process, to realize the best kinetic performance.

Nutrient removal with methanol as a carbon source full-scale continuous inflow SBR application.

Methanol was applied to a full-scale continuous inflow SBR, as a carbon source for denitrification and possible phosphorus removal. This research was conducted at the District of Kent Wastewater Treatment Plant in Agassiz, British Columbia, Canada. This plant employs two SBR's working in parallel; one unit was used as a control, without the addition of methanol. There was no difference in the overall total nitrogen removal efficiency through methanol addition, however,the additional carbon source significantly shortened the denitrification reaction time in the existing reactor. The high nitrogen removal efficiency, with or without methanol addition, was primarily due to the advantages provided by continuous-flow SBR carbon loading. The phosphorus removal efficiency in the experimental SBR was also consistently higher than in the control SBR. The solids production from methanol addition wa s estimated to vary between 0.18 and 0.29gVSS/gCH3OH. Methanol addition also had an influence on the settling qualities of the sludge.

Anaerobic acidogenesis of primary sludge: the role of solids retention time.

This research investigates the effect of solids retention time (SRT) on the acid-phase anaerobic digestion of primary sludge. A series of experiments were conducted using two continuous-flow 3-L units with the following configuration: a completely mixed reactor (CMR) with clarifier and solids recycle and an upflow anaerobic sludge blanket (UASB) reactor. Results show that C(2) to C(5) volatile fatty acids (VFA) were the predominant compounds formed. At a constant hydraulic retention time (HRT) of 12 h, variation in SRT from 10 to 20 days resulted in a slight increase in VFA production in both systems, but at a shorter SRT (5 days) a drastic drop in acid production was observed. In addition, the percent distribution of VFA was to some extent affected by the change in SRT. On the other hand, organic matter degradation [measured by the chemical oxygen demand (COD) specific solubilization rate or the percent volatile suspended solids (VSS) reduction] appeared to be independent of SRT, at least in the range investigated. The percent soluble COD in the form of VFA, however, increased steadily with increasing SRT, approaching the 90% level at 20 days. The remaining soluble COD in the effluent from these systems may be mainly attributed to metabolic intermediates and unused soluble substrate.

Determination of Poly-beta-Hydroxybutyrate and Poly-beta-Hydroxyvalerate in Activated Sludge by Gas-Liquid Chromatography.

A convenient gas-liquid chromatography procedure to quantify poly-beta-hydroxybutyrate and poly-beta-hydroxyvalerate in activated sludge was developed by combining lyophilization of the samples, purification of the chloroform phase by water reextraction, and the use of capillary columns. With a flame ionization detector the sensitivity was estimated at 10 g/liter.