Wastewater samples collected from seven wastewater treatment plants (WWTPs) were characterized to assess the impacts of wastewater cations on the activated sludge process. The cations included in this study were sodium (Na+), potassium, ammonium, calcium, magnesium, aluminum (Al), and iron (Fe). Among the selected cations, Al and Fe were of most interest to this study because their role in bioflocculation has not been extensively studied and remains largely unknown. The data showed that WWTPs contained highly varying concentrations of Na+, Al, and Fe in the wastewater and that these cations were responsible for differences between WWTPs as to sludge dewatering rates and effluent quality. In general, a high influent Na+ concentration caused poor sludge dewatering and effluent characteristics. However, when sufficient Al and Fe were present in floc, the deleterious effects of Na+ were offset. The data associated with Al further revealed that waste activated sludge with low Al contained high concentrations of soluble and colloidal biopolymer (protein + polysaccharide), resulting in a high effluent chemical oxygen demand, high conditioning chemical requirements, and poor sludge dewatering properties. These results suggest that Al will improve activated sludge effluent quality by scavenging organic compounds from solution and binding them to floc.
A combination of bench scale and full-scale studies were conducted to determine the effectiveness of high intensity mechanical shear in an internal recycle loop to enhance mesophilic anaerobic digestion and its implications for routine operations of a digestion system. During short-term batch studies (56-hours) a 46% increase in biogas production was observed. In long term batch studies (20-days) there was an observed 15% increase in biogas production and increased volatile solids destruction. The observed increase in digestion efficiency was supported by a full-scale demonstration, in which increased total and volatile solids destruction was observed, 22% and 21% for the primary digester and 17.2% and 11% for the secondary digester respectively. The data also suggests that protein degradation is one of the major mechanisms associated with the observed increases in volatile solids destruction. The full-scale demonstration also determined that shear enhanced digestion can be operated without process upset, based on volatile fatty acid profile and headspace biogas composition (methane and carbon dioxide). Dewatering properties as measured by polymer demand were deteriorated in the primary digester while there was an apparent improvement in the secondary digester. High intensity shear does not appear to enhance pathogen reduction based on indicator organisms, total and fecal coliforms.
The role of iron and aluminium in determining volatile solids reduction and odors from anaerobically digested, dewatered sludge cakes was evaluated from data collected from a variety of wastewater treatment plants. It was found that volatile solids reduction generally increased as the iron content of the sludge increased. It was also observed that odors increased with increasing iron. No correlation with aluminium or divalent cations was found. Based on these data it appears that the volatile solids reduction by anaerobic digestion is not useful for predicting the odors from anaerobically digested sludges.
We present an efficient, bright, and robust source of photons at the rubidium D1-line (795 nm) with a narrow bandwidth of δ = 226(1) MHz. The source is based on non-degenerate, cavity-enhanced spontaneous parametric down-conversion in a monolithic optical parametric oscillator far below threshold. The setup allows for efficient coupling to single mode fibers. A heralding efficiency of η heralded = 45(5) % is achieved, and the uncorrected number of detected photon pairs is 3.8×10 3 cts/(s mW). For pair generation rates up to 0.5 MHz, the source emits heralded single photons with negligible contamination from higher photon number states as evidenced by g(2) c < 0.01. The source is intrinsically stable due to the monolithic configuration. Frequency drifts are on the order of δ /20 per hour even without active stabilization. By applying mechanical strain, the source frequency can be fine-tuned within a range of ≥ 2 GHz.
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