Reduction of waste biosolids by RAS-ozonation: Model validation and sensitivity analysis for biosolids reduction and nitrification

Biosolids reduction model by return activated sludge ozonation was validated by simulating nitrification data compiled from our pilot-scale and the literature studies. Then, a global sensitivity analysis (GSA) was performed to identify influential and non-influential parameters for biosolids reduction efficiency, change in specific nitrification activity (SNA), and alteration to expected nitrification stability. In general, the model outputs were sensitive to operational and ozone reaction parameters, but not to biochemical parameters. For operational parameters, mainly temperature and initial solids retention time (SRT) influenced all model outputs. For biosolids reduction, increase in the degradability of the influent COD decreased the reduction efficiency. For SNA, the changes were highly dependent on the influent TKN/COD ratio. Our findings also imply that the stability of the nitrification process in ozonated systems should be enhanced at constant MLVSS for warm temperatures, but could be reduced at temperatures below 12 °C and aerated SRTs below 10 days.     

Pilot Plant Study of Simultaneous Sewage Sludge Digestion and Metal Leaching

This research is related to a preindustrial pilot scale study of the performance of the simultaneous sewage sludge digestion and metal leaching (SSDML) process for decontamination and stabilization of sewage sludge. Ten batch tests were carried out in two 4?m3 bioreactors under various conditions of operation. Results indicated that the addition of 1.0 to 1.5?g?S0/L, which is the equivalent of approximately 30 to 50?kg?S0 per tons dry sludge, is sufficient to obtain conditions of acidity (pH<2.5) and oxido-reduction potential greater than 500 mV necessary for an effective solubilization of toxic metals. The final average of metal solubilization in the output sludge during the SSDML process varied in the following ranges: 25–78% Cd, 9–32% Cr, 48–100% Cu, 77–99% Mn, 15–53% Ni, 12–47% Pb, and 66–100% Zn. The N, P, and K contents were also preserved in the decontaminated sludge. Moreover, the use of low concentrations of elemental sulfur makes it possible to obtain decontaminated sludge with a low total sulfur content (1.4–1.5% S) compatible with agricultural use. The suspended solids removal calculated for the SSDML process was slightly lower, (2.5±0.4)% volatile suspended solids per day, than those reached using standard aerobic digestion. Finally, the SSDML process was found to be effective in removing bad odors and in the destruction (99–100%) of indicator bacteria.     

Off-Site Exposure to Respirable Aerosols Produced during the Disk-Incorporation of Class B Biosolids

Field experiments were conducted at a Class B biosolids land application site in central Arizona to measure, model, and source-track the off-site transport of aerosols emitted when biosolids were disk-incorporated into soils. Real-time PM10 monitoring provided time-resolved aerosol information sufficient for verifying both off-site concentration and off-site exposure time model results. Under the conditions considered and at a distance of 165?m from the aerosol source, biosolids disk-incorporation resulted in an intermittent exposure to biosolids-derived aerosol concentration between 15 and 40?μg/m3 and an inhalable biosolids dose between 2 and 8?μg. Transport modeling predicted that these doses will decrease with increasing wind speed. In addition, three DNA sequence-based biosolids source tracking methods were applied to aerosol samples and confirmed the presence of biosolids in aerosols at 5, 65, and 165?m from the aerosol source. Field measurements and modeling indicate that the nature of biosolids-derived aerosol exposure is a series of intermittent high concentration puffs, rather than a continuous low concentration.     

PWR核电站蒸汽发生器停堆湿保养工况联氨的缓蚀作用

一、引言压水堆(PWR)核电站蒸汽发生器(SG)管材因二回路系统腐蚀产物积累发生应力腐蚀开裂,这是SG传热管破损的主要原因之一。维修和更换SG使PWR停运期间所需要的替用电力对发电站造成很大的财政负担,同时,二回路系统的腐蚀产物沉积在蒸汽发生器内,降低     

Domestic and Industrial Wastewater Treatment with Ozonated Activated Sludge

Poor sludge settleability is a problem encountered in many activated sludge wastewater treatment plants. This study was aimed at combatting the unwanted biological growths at the root of this phenomenon with ozone. Ozone dosed directly into the aeration basins of small activated sludge pilot plants treating both domestic and synthetic fuel wastewaters led to a substantial reduction of the bulking problem even at dosages as low as 6 to 10 mg/L. Ozone did not interfere in the delicate nutrient removal processes and significantly enhanced effluent quality.     

Dewatering behaviour of water treatment sludges associated with contaminated site remediation in Antarctica

Sludge reduction and dewatering is an important aspect of water and waste water treatment. This is especially true in the case of Australia's Antarctic contaminated site remediation program, where the reduction in volume of wastes to be returned to Australia can lead to significant transport and handling cost savings. The dewatering characterisation of water treatment sludges from an Antarctic contaminated site was conducted using a theory of suspension dewatering developed by Buscall, Landman and White. This theory uses fundamental material properties of compressibility and permeability to determine the diffusivity of a suspension. Diffusivity is a useful property that can be used to directly compare the dewaterability of various sludges. In this investigation, several water treatment sludges were collected and characterised in the field to determine the impact of temperature and additives on compressibility, permeability and diffusivity. The Antarctic sludges were found to be less compressible and less permeable than materials such as mineral suspensions and alum water treatment sludges. Compressibility was found to decrease with the addition of powdered coagulation aids such as bentonite and chitosan.     

MOBILIZATION OF SLUDGE IN HORIZONTAL CYLINDRICAL TANKS WITH SUBMERGED NOZZLES

Over 378,000 m³ (100 million gal) of radioactive waste is being stored in hundreds of tanks at several U.S. Department of Energy (DOE) sites. The environment within the tanks is highly radioactive and chemically harsh. The waste typically consists of a heterogeneous sludge layer covered by a layer of supernatant. A few of the tanks have leaked to the environment, while others are corroding. Removing the waste from the tanks and processing it to a stable final form are desired to prevent any additional contamination of the environment. The tanks vary in size and geometric shape and do not have systems for removing the sludge waste.

Mobilization and mixing studies were conducted with a surrogate sludge (e.g., kaolin clay) using submerged jets in two sizes of horizontal tanks with nominal capacities of 0.87 m³ (230 gal) and 95 m³ (25,000 gal). Mobilization efficiencies and mixing times were determined for single and bidirectional jets in both tanks with the discharge nozzles positioned at various locations in the tanks. Approximately 80% of the surrogate sludge was mobilized in the 95-m³ tank using a fixed bidirectional jet (inside diameter = 0.035 m) and a jet velocity of 6.4m/s (21 ft/s). The effective cleaning length, which is defined as the distance between the jet and the edge of the remaining sludge bank, was approximately 3.2 m (10 ft) on each side of the bidirectional jet.     

Feasibility of Sludge Ozonation for Stabilization and Conditioning

A pilot-scale sludge treatment plant was built to investigate the feasibility of ozonation processes for waste activated sludge treatment. Ozonation of wastewater sludge resulted in mass reduction by mineralization as well as by supernatant and filtrate recycle. Another advantage of sludge ozonation is a significant improvement of settleability and dewaterability. Experimental results showed that mass reduction of 70% and volume reduction of 85% compared with the control sludge was achieved through the sludge ozonation at a dose of 0.5?gO₃/gDS. It is also interesting to note that the filterability deteriorates up to ozone dose of 0.2?gO₃/gDS and then improves considerably at a higher ozone dose. The filterability could be improved by chemical conditioning even at a low ozone dose. The economic feasibility by cost analysis reveals that ozonation processes can be more economical than other alternative processes for sludge treatment and disposal at small-sized wastewater treatment plants.     

Effect of clinoptilolite addition and solids retention time on the extracellular polymeric substances composition and soluble chemical oxygen demands in activated sludge

This study was carried out to compare EPS (Extracellular Polymeric Substances) composition between conventional activated sludge (AS) and activated sludge dosed with clinoptilolite (CAS). Additionally, those were compared with organic removal efficiency in the effluent in conjunction with EPS concentrations. The experiments were conducted at SRT (Solids Retention Time) ranging from 5 to 100 d. For the CAS, proteins were more readily observed for SRT 20 and 100 d compared to that of the AS. Polysaccharide concentration in the sludge was greatly increased for the CAS, but it was significantly diminished when the SRT was extended. The level of EPS concentration observed from the effluent had the same pattern of variation for the two different types of systems. Regardless of type of reactor, the ratio of proteins for sludge versus effluent was independent of SRT, but the ratio of polysaccharides diminished as SRT increased. In the long run, the degree of protein synthesis directly ascribed to concurrent enhancement of SCOD removal efficiency was slightly more in the CAS. It was decided that clinoptilolite added system could be more reliably retrofitted to a conventional activated sludge process.