Precipitation and recovery of phosphorus from the wastewater hydrolysis tank.

Phosphorus, a limited resource, is also an environmental pollutant that should be removed from wastewater and ideally reused. A pilot-scale facility was set up and used to precipitate and recover phosphorus from wastewater. The return activated sludge in a hydrolysis tank was flocculated and separated and the solid material returned to the hydrolysis tank; the flocculation process did not harm the microorganisms. Phosphate in the reject water was precipitated with different calcium salts and the phosphorus-containing precipitate recovered. The precipitate consisted mainly of phosphate and calcium, and under 5% of the final product consisted of iron and aluminum. Around 20% of the precipitate was organic material. The pilot-scale test was supplemented with bench-scale tests using calcium salt, magnesium salt, and NaOH/KOH. Without the addition of calcium ions, phosphate could be precipitated by increasing pH to 9.5, resulting in a concentration of phosphorus in the reject water of under 2 mg/L. If calcium salt was added (Ca:P ratio of 2:1), it was possible to remove phosphate at pH 9 (<1 mg/L). In general, the concentration of dissolved phosphate was 8-10 mg/L lower after precipitation when calcium salt was used compared with all other tested salts. This difference increased if additional phosphate was added to the sludge. The bench- and pilot-scale experiments yielded comparable data. At the pilot-scale facility, it was possible to remove 90% of the phosphate by adding calcium salt and regulating the pH to 8.5.

Revealing the importance of meristems and roots for the development of hypersensitive responses and full foliar resistance to Phytophthora infestans in the resistant potato cultivar Sarpo Mira.

The defence responses of potato against Phytophthora infestans were studied using the highly resistant Sarpo Mira cultivar. The effects of plant integrity, meristems, and roots on the hypersensitive response (HR), plant resistance, and the regulation of PR genes were analysed. Sarpo Mira shoots and roots grafted with the susceptible Bintje cultivar as well as non-grafted different parts of Sarpo Mira plants were inoculated with P. infestans. The progress of the infection and the number of HR lesions were monitored, and the regulation of PR genes was compared in detached and attached leaves. Additionally, the antimicrobial activity of plant extracts was assessed. The presented data show that roots are needed to achieve full pathogen resistance, that the removal of meristems in detached leaves inhibits the formation of HR lesions, that PR genes are differentially regulated in detached leaves compared with leaves of whole plants, and that antimicrobial compounds accumulate in leaves and roots of Sarpo Mira plants challenged with P. infestans. While meristems are necessary for the formation of HR lesions, the roots of Sarpo Mira plants participate in the production of defence-associated compounds that increase systemic resistance. Based on the literature and on the presented results, a model is proposed for mechanisms involved in Sarpo Mira resistance that may apply to other resistant potato cultivars.

Differential gene induction in resistant and susceptible potato cultivars at early stages of infection by Phytophthora infestans.

Sarpo Mira, a potato variety with high resistance against the late blight pathogen Phytophthora infestans, is being used in breeding programs to increase late blight resistance in commercial varieties. Discovering genes that are important for P. infestans resistance will assist in the development of molecular markers for the selection of new resistant cultivars and the use of resistant varieties will reduce the environmental, health and financial costs associated with the use of pesticides. Using complementary DNA amplified fragment length polymorphism analyses, differentially expressed genes involved in the potato-P. infestans interaction were identified in the susceptible Bintje and in the resistant Sarpo Mira potato cultivars. Forty-eight differentially expressed transcript derived fragments (TDFs) were cloned and sequenced. The expression profiles of some of these genes were analyzed in detail using quantitative RT-PCR at seven time points: 1, 4, 17, 24, 30, 41 and 65 hours after inoculation (hai). We found that five transcripts with homologies to pathogenesis/defense-related genes and two TDFs with homology to transcription factors were significantly induced to higher levels in the resistant cultivar at very early stages of the infection (1 hai). Interestingly, most of these genes showed different expression profiles throughout the whole infection process between both cultivars. Particularly during its biotrophic growth phase, P. infestans triggered the down-regulation of infection responsive genes in the susceptible but not in the resistance cultivar. Our results suggest that these newly identified early-induced transcripts may be good candidates for conferring Sarpo Mira's resistance to late blight and they could be useful molecular markers for the selection of new resistant cultivars.