We tested at full-scale the innovative Focused Pulsed (FP) technology for pre-treating waste sludge in order to improve methane gas production and biosolids reduction in sludge digestion, but without incurring problems of odors, toxicity, and high costs for chemical or energy consumption. FP pre-treatment of a mixture of primary and secondary sludge increased the soluble COD by 160% and DOC 120% over the control. FP pre-treatment of 63% of the input waste sludge increased biogas production by over 40% and reduced biosolids requiring disposal by 30% when compared to the plant baseline. FP pre-treatment also correlated with a shift of the bacterial and archaeal communities. The most significant change was that the acetate-cleaving Methanosaeta became the dominant methanogen. Full FP pre-treatment should increase biogas production and biosolids removal by 60% and 40%, respectively. Full FP pre-treatment should generate energy benefits of at least 2.7 times and as high as 18 times the FP energy input, depending on heat recovery from FP treatment. For a plant treating 76,000 m3/d of wastewater (380 m3-sludge/d), FP treatment should generate an annual economic benefit of approximately $540,000 net of electricity and other operating and maintenance costs. This represents a payback period of three years or less.
This work investigates how chemical speciation controls
the toxicity of neptunium and the neptunium−NTA
complex toward Chelatobacter
heintzii. We
studied the
effect of aquo and complexed/precipitated neptunium on the
growth of C. heintzii in noncomplexing glucose
and
phosphate-buffered nitrilotriacetic acid (NTA) growth
media.
Equilibrium chemical speciation modeling and
absorption
spectroscopy were used to link neptunium speciation to
biological growth inhibition. Our results show that
metal
toxicity of aquo NpO2
+ significantly limits
the growth of C.
heintzii at free metal ion concentrations greater
than
≈10-5 M. However, neptunium
concentrations ≥10-4 M
do not cause measurable radiotoxicity effects in C.
heintzii
when present in the form of a neptunium−NTA complex or
colloidal/precipitated neptunium phosphate. The neptunium−NTA complex, which is stable under aerobic condi
tions, is destabilized by microbial degradation of NTA.
When phosphate was present, degradation of NTA led to
the precipitation of a neptunium-phosphate
phase.
A wastewater-treatment flowsheet was developed to integrate uniquely designed biological processes with physical-chemical unit processes, allowing conversion of the organic carbon in the wastewater to methane, the removal and recovery of phosphorus and nitrogen from the wastewater, and the production of water suitable for reuse. In the flowsheet, energy is derived from the wastewater by first shunting a large fraction of the organic carbon in the wastewater to a solids slurry which is treated via anaerobic digestion. The anaerobic digestion system consists of focused pulsed (FP) pretreatment coupled to anaerobic membrane bioreactors (MBRs). Computer modelling and simulation results are used to optimize design of the system. Energy generation from the system is maximized and costs are reduced by using modest levels of recycle flow from the anaerobic MBRS to the FP pretreatment step.
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