28 The removal characteristics of natural organic matter in the recycling of drinking water treatment sludge: Role of solubilized organics
This paper, written by researchers from Beijing industry University and others, discusses The removal characteristics of natural organic matter in the recycling of drinking water treatment sludge: Role of solubilized organics. The paper is published in an important journal < Ultrasonics Sonochemistry >. IF：6.012.
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To clarify the role of solubilized organics derived from drinking water treatment sludge (DWTS) in the elimination of natural organic matter (NOM) in the DWTS recycling process, a probe sonoreactor at a frequency of 25 kHz was used to solubilize the organics at varied specific energies. The coagulation behavior related to NOM removal in recycling the sonicated DWTS with and without solubilized organics was evaluated, and the effect on organic fractionations in coagulated water was determined. The study results could provide useful implications in designing DWTS recycling processes that avoid the enrichment of organic matter. Our results indicate that DWTS was disrupted through a low release of soluble chemical oxygen demand (SCOD) and proteins, which could deteriorate the coagulated water quality under the specific energy of 37.87–1212.1 kW h/kg TS. The optimal coagulation behavior for NOM removal was achieved by recycling the sonicated DWTS without solubilized organics at 151.5 kW h/ kg TS specific energy. Recycling the sonicated DWTS could increase the enrichment potential of weakly hydrophobic acid, hydrophilic matter, and <3 kDa fractions; the enrichment risks could be reduced by discharging the solubilized organics. Fluorescent characteristic analysis indicated that when recycling the sonicated DWTS without solubilized organics, the removal of humic-like substances was limited, whereas removal of protein-like substances was enhanced, lowering the enrichment potential of protein-like substances.
The main conclusions drawn from this work are as follows: (1) DWTS was disrupted by the relatively low release of SCOD and proteins, which could deteriorate the coagulated water quality under the specific energy input of 37.87–1212.1 kW h/kg TS. (2) The most desirable coagulation behavior in regards to NOM removal was achieved by recycling sonicated DWTS without solubilized organics, which could be achieved with a specific energy of 151.5 kW h/kg TS. (3) The main organic fractionations in recycled DWTS were WHoA and HiM, with the MW >100 kDa and <3 kDa. Recycling sonicated DWTS containing solubilized organics could increase the enrichment potential of WHoA, HiM, and <3 kDa fractions. By discharging the solubilized organics this enrichment risk could be reduced. (4) Fluorescent characteristic analysis confirmed that both humic-like (peak A) and protein-like (peak T1) substances were released into the supernatant of sonicated DWTS. By discharging the solubilized organics in the recycled sonicated DWTS, the humic-like substances could not increasingly be removed, whereas the enhanced removal of protein-like substances could be achieved, lowering the enrichment potential of protein-like substances. (5) A useful strategy using ultrasound as a pretreatment of DWTS and then discharging the solubilized organics was recommended to avoid the organic enrichment risk of the DWTS recycling process.
A probe-type sonoreactor (XH-2008DE, Xianghu Ultrasonic Instrument Co., Beijing, China) operating at a fixed frequency of 25 kHz and a nominal power output up to 1500 W, was used to solubilize extracellular or intracellular organics derived from DWTS. 100 ml raw DWTS samples were placed in a double-wall, jacketed glass container and subjected to continuous ultrasound irradiation emitted through a 18 mm diameter tip at a power input ranging from 100W to 400 W, under the ultra-sonication time of 20 min, corresponding to the specific energy of 303.0–1212.1 kW h/kg TS. The ultra-sonication time (2.5, 5, 7.5, 10, and 15 min, respectively) was also looked at with an energy density of 1W/ml, corresponding to the specific energy of 37.87–303.1 kW h/kg TS. During each ultra-sonication experiment, the samples were mixed using a magnetic stirrer at 250 rpm. The raw DWTS volume remained constant at 100 ml, and neither temperature nor pH was regulated.