The Influence of Carbon Source Types and Nitrate on the Performance of the Enhanced Biological Phosphorus Removal Systems

This research focuses on two issues in enhanced biological phosphorus removal (EBPR). The first issue encompasses the effect of the type of carbon sources (i.e. volatile fatty acids and non volatile fatty acids) on the microbiology of EBPR. The second issue deals with the influence of denitrification on EBPR. Few studies have been performed to investigate these two issues. The recent findings on these areas are summarized below to establish the knowledge gaps this dissertation attempted to address. Details on the specific findings can be found in the literature review portion of this proposal

Influence of Various Mulching Materials on Evapotranspiration, Root Distribution, Soil Moisture and Temperature

博士論文 (Doctoral dissertation

Microbial Selection on Enhanced Biological Phosphorus Removal Systems Fed Exclusively with Glucose

The microbial selection on an enhanced biological phosphorus removal (EBPR) system was investigated in a laboratory-scale sequencing batch reactor fed exclusively with glucose as the carbon source. Fluorescence In Situ Hybridization analysis was performed to target two polyphosphate accumulating organisms (PAOs) (i.e., Candidatus Accumulibacter phosphatis and Microlunatus phosphovorus) and two glycogen accumulating organisms (GAOs) (i.e.,Candidatus Competibacter phosphatis and Micropruina glycogenica). The results show that glucose might not select for Candidatus Accumulibacter phosphatis. However, Microlunatus phosphovorus, Candidatus Competibacter phosphatis, and Micropruina glycogenica might be selected. The highest percent relative abundance (% RA) of Candidatus Accumulibacter phosphatis was about 42%; this occurred at the beginning of the experimental period when phosphorus removal was efficient. However, the % RA of these bacteria decreased, reaching below 4% at the end of the run. The maximum % RA of Microlunatus phosphovorus,Candidatus Competibacter phosphatis, and Micropruina glycogenica was about 21, 37, 17%, respectively. It appears that a higher glucose concentration might be detrimental forMicrolunatus phosphovorus and Micropruina glycogenica. Results also indicate a dominance of GAOs over PAOs when EBPR systems are fed with glucose. It is possible that the GAOs outcompete the PAOs at low pH values; it has been reported that at low pH, GAOs use glycogen as the energy source to uptake glucose. As a result, P-removal deteriorated. Therefore, glucose is not a strong candidate as a carbon source to supplement EBPR systems that do not contain sufficient volatile fatty acids

Impacts of Carbon Source Addition on Denitrification and Phosphorus Uptake in Enhanced Biological Phosphorus Removal Systems

In this study, simultaneous denitrification and phosphorus (P) removal were investigated in batch tests using nitrified mixed liquor and secondary wastewater influent from a full-scale treatment plant and different levels of acetate and propionate as supplemental carbon sources. Without supplemental carbon source, denitrification occurred at low rate and P release and P uptake was negatively affected (i.e., P removal of only 59.7%). When acetate and propionate were supplied, denitrification and P release occurred simultaneously under anoxic conditions. For acetate and propionate at a C/N stoichiometric ratio of 7.6, P release was negatively affected by denitrification. For acetate, the percent P removal and denitrification were very similar for C/N ratios of 22 (5X stoichiometric) and 59 (10X stoichiometric). For propionate, both percent P removal and denitrification deteriorated for C/N ratios of 22 (5X stoichiometric) and 45 (10X stoichiometric). It was observed that carbon source added in excess to stoichiometric ratio was consumed in the aerobic zone, but P was not taken up. This implies that PAO bacteria may utilize the excess carbon source in the aerobic zone rather than their polyhydroxyalkanoate (PHA) reserves, thereby promoting deterioration of the system

Morphological Changes of Placenta in Preeclampsia

Context: Preeclampsia is regarded as a risk factor in pregnancy and it leads to placental insufficiency. This, in turn causes both maternal and fetal morbidity and mortality. The present study intends to compare the morphological changes of placenta in preeclampsia with that of normal placenta. Study design: A descriptive type of study

The influence of actively growing roots and root exudates on nitrogen mineralization from soil organic matter in paddy rice soils

As plants interact with the soil to acquire and mobilise nutrients, their roots alter the soil biologically, chemically and physically over variable distances from its surface, defining the extent of the rhizosphere by the respective processes considered in space and time (Paterson, 2003). To date, very little is known on the influence of root growth and rhizodeposition of root exudates (i.e. mainly sugars and polysaccharides, organic and amino acids, peptides and proteins) on N turnover in paddy rice soils. Classical N mineralization experiments are done using uncropped soil, thus completely neglecting the influence of roots and root exudates on the N mineralization process. In this research we explicitly have taken into account this influence. Two experiments were conducted, one is an incubation experiment with artificial root exudates and the other, is a pot experiment with actively growing rice crops. In the first experiment, the effects of rice root exudates on net nitrogen mineralization were investigated in a six week incubation study at 25°C with three different paddy soils from Bangladesh under saturated conditions. This study consisted of four different treatments with artificial root exudates applications, namely (1) low molecular weight organic acids (a mixture of malic, tartaric, succinic, citric and lactic acid at a C-ratio of 80:9:5:4:2), (2) carbohydrates (glucose), (3) a mixture of organic acids and carbohydrate solutions (at a C-ratio of 50:50) along with a (4) control. Root exudates were artificially injected into the soil column at three fixed locations each week at a rate of 103 µg C g-1 week-1. An inconsistent treatment effect was found on the nitrogen mineralization over three different rice soils under saturated condition. In only one of the three studied sites, enhanced N mineralization was observed in all amended treatments. Hence the stimulatory effect on the N mineralization might derive from a ‘priming effect’. A second experiment was conducted to investigate the influence of rice roots on nitrogen mineralization from soil organic matter. Five selected soils from Bangladesh were filled in large plastic boxes (e.g. 0.4*0.6*0.2m) with 15 kg in each boxes and brought under saturated condition. Thirty five days old seedlings were transplanted in the plastic boxes. During the entire growing period, soil samples were taken to measure the mineralized NH4+ and NO3- at every two weeks interval from three spots of each plastic box at the middle of two hills with the help of a small augur. The total N uptake by the crop was measured at two occasions (during 35 days after transplanting and harvesting period). In four out of five soils, the sum of the N uptaken by the crop and N mineralization in cropped soil was found to be higher than the N mineralization in uncropped soils. Higher N mineralization in cropped soils than the uncropped soils suggests that there is a positive effect of actively growing roots on N mineralization. However, more experimental research is ongoing to reach a concrete conclusion

Indicators for N mineralization in paddy rice soils in Bangladesh

The N requirement for paddy rice cultivated in Bangladesh amounts to approximately 45-80 kg N ha-1. Lack of knowledge on N mineralization from soil organic matter (SOM) leads farmers to fill up this N requirement exclusively by costly mineral fertilizers, which have typically an efficiency of less than 50%. After decades of searching for a practical tool to estimate the N mineralization capacity of soil, there is still no consistent methodology. We assessed different physical and chemical fractions of soil organic matter (SOM) as predictors for the net N mineralization measured from aerobic (field capacity) and anaerobic (saturated) soil cores in 100 days laboratory incubations. First, N mineralization and C and N were assessed from long-term experimental plots of a highly weathered ‘terrace soil’ and a younger fluvisol, involving combinations of mineral fertilizer dressings and OM application. A positive correlation between N mineralization and soil N content, which was clearly related to management, was found for the terrace soil while no correlation was found for the fluvisol. Instead a strong negative relationship with soil OC content suggests a simultaneous accumulation of SOC and immobilization of N in this soil. Hence the relation between OM management for SOM accumulation and availability of N through mineralization is not straightforward in different soils in Bangladesh. Therefore other predictors than soil N content or C:N ratio were investigated . A soil set consisting of 29 paddy rice fields were physically fractionated into particulate OM (POM) and silt and clay associated OM following mild ultrasonic dispersion and wet sieving. The silt and clay sized OM was further chemically fractionated by oxidation with 6% NaOCl to isolate an oxidation-resistant OM fraction, followed by extraction of mineral bound OM with 10% HF thereby isolating the HF-resistant OM (NaOCl-res. HF-res.OM). A parallel fractionation scheme involved a ‘thermal fractionation’ by sequential water extraction at 100, 150 and 200°C via accelerated solvent extraction. Several physical and chemical fractions correlated positively with the linear fitted aerobic N mineralization rate, while no correlations were observed with anaerobic mineralization. The R2 values of linear regressions between N content of the physicochemical fractions and aerobic N mineralization rate were, however, lower than the R2 found for bulk soil N content. ‘Thermal fractionation’ yielded two fractions which correlated better with aerobic N mineralization, namely the 100+150°C extractable N and 200°C extractable N, but the R2 were close to bulk soil N. In conclusion, while some useful predictors for aerobic N mineralization were found, insight in the anaerobic N mineralization is lacking. Further research into importance of soil mineralogy, surface area, soil texture, etc. will be needed to increase our understanding of anaerobic mineralizatio

The influence of artificial root exudates on nitrogen mineralization in paddy rice soils under saturated conditions

Plant roots exude a wide range of low molecular weight organic compounds in to the rhizosphere, which undoubtedly influences N turnover. However, the exact influence of these organic compounds on nitrogen mineralization is yet unknown. The effects of rice root exudates on net nitrogen mineralization were investigated in a six week incubation study at 25°C of three different rice soils from Bangladesh under saturated conditions. This study consisted of four different treatments with artificial root exudates applications, namely (1) low molecular weight organic acids (a mixture of malic, tartaric, succinic, citric and lactic acid at a C-ratio of 80:9:5:4:2), (2) carbohydrates (glucose), (3) a mixture of organic acids and carbohydrate solutions (at a C-ratio of 50:50) along with a (4) control. Root exudates were artificially injected into the soil column at three fixed locations each week at a rate of 103 µg C g-1soil week-1. An inconsistent treatment effect was found on the nitrogen mineralization over three different rice soils under saturated condition. Therefore, this effect of artificial root exudates seems to be site specific. In only one of the three studied sites, enhanced N mineralization was observed in all amended treatments. Hence the stimulatory effect on the N mineralization seems to derive from a ‘priming effect’