Inge Nilsson

Denitrification of Water Using Immobilized Pseudomonas denitrificans Cells

SummaryPreparations of living Pseudomonas denitrificans cells immobilized in alginate gel were used in the denitrification of water. In the presence of an exogenous carbon source the entrapped microorganisms reduced nitrate and nitrite to gaseous products and to achieve complete reduction, carbon to nitrogen ratios of over two were required. The effects on denitrification of particle size and the number of bacteria in the gel were investigated. Apparent Km values for nitrate and nitrite reduction were calculated for free and immobilized cells. When the immobilized cells were incubated in nutrient media, an increase in reduction rate was observed and this was shown to be caused by the growth of cells within the gel particles. Immobilized P. denitrificans cells retained 75% of their initial nitrate reduction capacity after 21 days of storage at +4°C. The operational stability of the alginate-immobilized cells was studied both in batch and in a column which was operated continuously. A column (45 g of alginate-cell fibers in 80 ml) denitrified a high nitrate drinking water (100 mg NO3/l) with a rate of 300 ml of nitrate and nitrite free water/day/g of gel. The half life for nitrate reduction was estimated to be 30 days.

Columnar denitrification of water by immobilized Pseudomonas denitrificans cells

SummaryWhole cells of Pseudomonas denitrificans, immobilized in alginate gel, were used for columnar denitrification of ground water. Ethanol was selected as a suitable carbon source and the C/N-ratio necessary for satisfactory nitrate reduction was established (1.6 mg ethanol-C/mg nitrate-N). The course of the reaction and the diffusional limitations were investigated during columnar denitrification. The mechanical integrity of the gel matrix, as judged from leakage of cells was studied. The release of cells into the effluent was effectively inhibited (<102 cells/ml) by the use of different filter devices. The operational characteristics were determined by studying a column operating for nearly four months. Theoretically, the alginate gel column should, from high nitrate drinking water (22 mg NO3−-N/1), produce 3 1 of denitrified water/kg gel/h (wet wt.) during a period of two months. The regeneration of nitrate reduction activity by means of activation in nutrient media proved a useful tool for restoring initial activity, the gel column having shown no loss in activity at the end of the operation period.

Comparison of the performance of a hollow-fiber microbe reactor with a reactor containing alginate entrapped cells

SummaryAlginate entrapped Pseudomonas denitrificans have been compared with cells confined in the outer space of a hollow-fiber membrane unit with respect to continuous denitrification of water. The hollow-fiber unit had a higher productivity as well as a stability similar to that of the alginate unit. A reduction of cell-leakage in the eluate was found in the hollow-fiber unit. The nitrogen gas produced could be removed by circulating the cell containing fluid over a hydrophobic membrane.

Immobilized cells in microbial nitrate reduction.

The microorganismPseudomonas denitrificans was immobilized in alginate. These immobilized cells were capable of reducing 0.8 mg NO3-/min/g wet weight of cells.

Biofilm build-up of Pseudomonas putida in a chemostat at different dilution rates

SummaryA test system was set up where the build-up of a biofilm on a defined surface could be studied in a carbon source limited chemostat.The attachment of P. putida ATCC 11172 to glass when growing on L-asparagine was studied at different dilution rates (specific growth rates) from 0.1 to 1.5 h−1 The number of attached colony forming units (cfu) increased with dilution rate from 1×106 cfu/cm2 at 0.1 h−1 to 4×107 cfu/cm2 at 1.0 h−1 and then the attachment decreased to about 6×106 cfu/cm2 at higher dilution rates (1.1–1.5 h−1). The number of attached cfu was measured after 24 h exposure. The value of the maximum specific growth rate in batch culture was 0.6 h−1.The total amount of attached cell-mass followed roughly the same pattern as the viable count.The viable count of the cells suspended in the growth medium showed its lowest value at the same dilution rate as resulted in maximum adhesion.It was shown that the effect of growth rate on the biofilm build-up of P. putida is significant, and ought to be borne in mind when continuous culture systems are set up and results evaluated.

Conversion of fat into yeast biomass in protein-containing waste-water

SummaryCandida tropicalis S001 was grown on the lipid fraction of a protein-containing waste-water in order to (i) remove fat from the water, and (ii) produre yeast biomass for feed. The yeast cells were separated from the waste-water by sedimentation. Defatted waste-water was used for methane production and gave a yield of a 0.3 m3 methane/kg reduced chemical oxygen demand. The maximum specific growth rate (µmax) of C. tropicalis growing on waste-water fat at pH 4.0 was 0.35 h−1; the fat content was decreased from 8 g/l to about 0.1 g/l within 24 h. In continous culture a corresponding reduction was maintained at dilution rates up to 0.36 h−1. The effect on growth of pH, temperature and CO2 concentration was studied with triolein as the major carbon source. The µmax was nearly constant (0.16 h−1) in the pH and temperature range of 3.2–4.0 and 30°–38° C, respectively; 10% CO2 was optimal for growth. Growth on triolein resulted in a biomass yield of 0.70 g dry weight/g fat.

Effect of different environmental parameters on the biofilm build-up of Pseudomonas putida ATCC 11172 in chemostat

SummaryThe influence of carbon source, cell concentration, oxygen tension, pH and temperature on the biofilm build-up of Pseudomonas putida ATCC 11172 was studied. The experiments were performed in a carbon and energy limited chemostat (asparagine). When the asparagine was replaced by glucose the biofilm build-up was decreasing.Cell concentration, oxygen tension or temperature did not to any significant degree affect the biofilm build-up. Temperature, however influenced the size of the suspended cells. The cell size successively increased with decreasing temperature. A similar change in cell size could be accomplished by increasing the dilution rate from 0.2 h−1 (small cells) to 0.7 h−1 (large cells).The biofilm build-up increased with increasing pH in the interval of 5.5–6.7. The viable count of the biofilm after 24 h exposure of test surface increased from 8×106 cfu/cm2 to 1.6×108 cfu/cm2 while the biomass increased by a factor of about 70.

Estimation of the biofilm formation ability of Pseudomonas putida in discrete samples from continuous culture

SummaryTest systems were set up in order to evaluate the ability of biomass from a continuous culture to form biofilms. A film-forming strain of Pseudomonas putida was used as the test organism. The adsorption of resting cells onto glass surfaces was measured in specially designed chambers containing 1 ml of cell suspension. Both the quantity and the physiological activity of the adsorbed cells, in terms of optical density after detachment and pH change of a substrate exposed to the adsorbed cells, were measured. The analysis of biomass from continuous cultures of Pseudomonas putida verified the suitability of the methods. Furthermore, other properties of importance to biofilm formation such as hydrophobicity and flocculation capacity of the cells were investigated.It was shown for samples deriving from different dilution rates that the cell adsorption rate drastically increased at dilution rates higher than the μmax of the culture. Simultaneously, higher values of hydrophobicity and flocculation capacity were observed.It was also shown that the age and thickness of the biofilm subsequently produced in the continuous culture influenced the metabolic activity per unit of biomass attached to the surface. The methods described in this investigation may facilitate the study of parameters important to biofilm formation as well as the metabolic activity of the attached biomass.