Maintaining and Controlling an Extrinsic Biofilm for Pathogen Removal in Dental Unit Water Lines

The control of biofilm formation is a major concern for industrial, environmental, and public health. Undesirable biofilms can harbor different disease-causing pathogens and shorten the operational life of different equipment. On the other hand, beneficial biofilms are also used in various applications and managing its growth and activity can be desirable. Killing the biofilm does not usually incorporate the removal of the dead biofilm structure that is adhered to the surface. Therefore, the aim of this thesis is to control biofilm formation; to be able to remove, inhibit, and enhance biofilm formation. This thesis investigated the use of norspermidine, D-amino acids, and selected enzymes for the control of biofilm formation. Biofilm was pre-grown in 96-well microtiter plates and the different treatments were applied for 24 h. Biofilm formation was quantified before and after treatments using crystal violet stain. The results obtained in this thesis showed that norspermidine had a dual effect on biofilms formation. A concentration of 1 mM norspermidine removed 39% of nonactive biofilm, while for active biofilm norspermidine enhanced the biofilm growth by 73%. D-amino acids can inhibit biofilm growth at a low concentration of 5 µM. The two D-amino acids used in this study, D-tryptophan (15 mM) and D-tyrosine (20 µM), removed 28% and 31% of biofilm, respectively. No clear synergetic effects were noticed from mixed D-amino acids treatment. The enzymes Savinase and Pectinex showed the highest biofilm removal among the different tested industrial enzymes. Savinase removed 68% and 84% while Pectinex removed 74% and 55% of biofilm formed by Bacillus species and Pseudomonas fluorescens, respectively. The optimized enzymatic treatment containing both Savinase (19.6 and 23.7 U/mL) and Pectinase (63.8 and 48.8 U/mL) showed the highest biofilm removal for Bacillus sp. biofilm at pH 6 and P. fluorescens at pH 8

Effects of compost age on the release of nutrients

Composted organic materials are applied to help restore disturbed soils, speed revegetation, and control erosion; these changes are generally beneficial for stormwater quality. Ensuring that nutrient release from compost is adequate for plant needs without degrading stormwater quality is important since composts release nitrogen at variable rates (1–3% of total N/yr) and the leaching process can extend for many years. The aim of this work was to understand the effect of compost age on the extent and rates of nitrogen release by conducting detailed rainfall simulation studies of one compost type at three different ages. Models describing temporal changes in nitrogen release to runoff during a single storm and across multiple storms were developed and applied to the runoff data. Nitrogen content (%) and bulk density of compost increased with the increase in compost age and total nitrogen release decreased with increasing compost age. The three rain simulations (storms) performed on each of the three compost ages show that nitrogen release declined each day of the repeated daily storms. A first-order kinetic model was used to estimate the amount of nitrogen remaining on compost after several storms

On the alpha activity of natural tungsten isotopes

The indication for the alpha decay of 180-W with a half-life T1/2=1.1+0.8-0.4(stat)+-0.3(syst)x10^18 yr has been observed for the first time with the help of the super-low background 116-CdWO_4 crystal scintillators. In conservative approach the lower limit on half-life of 180-W has been established as T1/2>0.7x10^18 yr at 90% C.L. Besides, new T1/2 bounds were set for alpha decay of 182-W, 183-W, 184-W and 186-W at the level of 10^20 yr.Comment: 16 pages, 8 figures, accepted in Phys. Rev.