For the purpose of enhancing the adsorption of natural organic matter (NOM) from water sources, commercially available powdered activated carbon (PAC) was further ground to produce PAC of micrometre-sized particles, and the effects of PAC size on adsorption of NOM were investigated. The micrometre-sized PAC (median particle diameter, 0.8 and 3.8 μm) removed NOM much better than did asreceived PAC (33 μm). Only one-tenth the dose of micrometre-sized PAC had the same effect as a full dose of the as-received PAC. The micro-grinding of PAC to micrometre sizes was effective at increasing its adsorption kinetics: adsorption of NOM to the micrometre-sized PAC reached 80% of equilibrium within only 1 min of contact time. The micro-grinding of PAC was also effective at increasing its adsorption capacity for NOM and polystyrene sulfonate-MW1800, but not for the small molecule phenol. This appeared to be due to an increase in mesopore surface area probably by fracture of ink-bottle pore structures during the micro-grinding. The micro-grinding enhanced the adsorption affinity of PAC for NOM that was strongly UV260-absorbent but not for NOM with low UV260 absorbance.
Manufacturer-supplied powdered activated carbon (PAC) was ground to produce submicrometre particles (0.8 and 0.6 m median diameter) for use as an adsorbent before microfiltration (MF) for drinking water treatment. Batch tests revealed that the microground PAC adsorbed natural organic matter (NOM) much more rapidly and had a higher adsorptive capacity than ordinary PAC. The water samples pretreated with the submicrometre PAC were subjected to MF, and the results of experiments with different PAC contact times revealed that a 1 min retention time was sufficient for adsorptive removal of NOM. The use of submicrometre PAC permitted not only shorter PAC contact times but also a 75% reduction in dose.
Submicron powdered activated carbon (PAC) rapidly adsorbed natural organic matter (NOM) fromwater samples: a batch test of the adsorption kinetics showed that the NOM concentration dropped substantially within 15 s and then leveled off. In a tubular flow reactor test, NOM removal after a 15 s contact time was almost the same as removal values attained at longer contact times. Laboratory-scale and bench-scale pilotplant ceramic microfiltration (MF) experiments with submicron PAC adsorption pretreatment were conducted to evaluate NOM removal and to examine the effect of the PAC on filterability. The laboratory scale MF experiment revealed that PAC adsorption pretreatment could be accomplished with a detention (2.4 s) that was much shorter than the time expected from the adsorption kinetics test. This result suggests that adsorption pretreatment for MF could be accomplished by adding the submicron PAC directly into the feed line to the membrane and that installation of a special PAC contactor before the membrane unit is unnecessary. Although micron PAC rather than submicron PAC was used unintentionally in the pilot plant experiment, these PAC showed much better NOM removal than normal PAC, and no adverse effects, such as transmembrane pressure buildup and reversible or irreversible membrane fouling, were observed.
Anaerobic digestion of anaerobic sewage sludge leads to the generation of methane gas and reduction of the sludge volume. Because conventional digestion requires a long time, the digestion facilities must be large. We studied decomposing volatile suspended solids (VSS) in sewage sludge, capacitating high acid generation rates and a high-speed methane evolution reactor to reduce retention time for anaerobic digestion. We also studied how to increase VSS reduction ratio by using bio-technology. The high-performance thermophilic two-phase digestion (HPTTD) process is proposed as a innovative digestion system which has high-rate reducing and high-ratio reduction of volatile suspended solids in sewage sludge. This thermophilic digestion process consists of sludge conditioning, acidification and methanation steps. In the sludge conditioning step, sewage sludge is conditioned with thermal treatment and dosed with a protolytic enzyme. In the next step, acidification, acid fermentation is carried out at 70°C; this temperature is higher than that of conventional fermentation (conventional thermophilic digestion process: 55°C). In the methanation step an anaerobic fixed-bed reactor is used. In the digestion experiments using excess sludge, we obtained a 30% higher VSS reduction ratio (78% at HPTTD process) than that of conventional mesophilic digestion,
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