Study On The Extraction And Properties Of Humic Acid From Municipal Sludge

This paper described thatin undigested and digested sludge of sludge disposal systems of a large sewage treatment plant as raw materia,in ultrasound-assisted conditions, usingthe method of alkaline lysis and acid precipitation to extractsludge humic acid（HA）and analysisingperformance of the purified product.Condition of extraction factors was researched（such as ratio of sludge and lye, concentration of NaOH） in the extraction rate of HA as an indicator; With factors which hadsignificant impact on extraction rate,orthogonal experimenthad designedto optimize the extraction process and its verifiedresultwas that undigested HA’s optimal extraction conditions: NaOH concentrationwas 0.6 mol/L,ultrasonic time was10 min, ultrasonic power was 312.5W, acid precipitation to pH=1.5, in this condition, the extraction rate of undigested HAwas 90.3% and its mass score was 81.30%; digested HA’s optimal extraction conditions: NaOH concentration was 0.3 mol/L, added amountof 10% HClwas 7.5mL, extraction temperature was 30℃, acid precipitation to pH = 2.5, in this condition, the extraction rate of digested HAwas 92.3% and its mass score was 83.12%.By IR、elemental analysis、SEM、GPC、UV-visible spectrum and flocculation limit method, the perforance of the two HA products which were purified was researched. The results showed that both HA arecomposed of five elementsby C、H、 O、 N and S;The structurearecomposed ofa large number of aromatic and aliphatic compounds such as phenolic hydroxyl group、alcoholic hydroxyl group、nitro; Undigested and digested HA’s weight average molecular weight are 27095 and 25156 respectively; Compared with the mineral source HA, functional group of sludge HAhas more types（for example: a peptide bond, a sulfo group, an ether bond, amide）and it haslower molecular weight; thus, the sludge HA has an apparent biochemical characteristics of humic acid.Two kinds of HA’s surfacestructure arerough and loose and has great porosity, which may provides a favorable adsorption voids and channels as well as other uses.The UV spectrum of two HA is monotonous and no characteristic, which only in the vicinity of 210 nm has an absorption peak derived from aromatic structure. Sludge HA molecules contains more aromatic groups, however, mineral source HA contains more aliphatic chain structure. The content of oxygen-containing functional groups of digested HAis larger than undigested HA and HA which are extracted from soils and sediments.Through anaerobic digestion process of microbial, digested HA has a higher degree of humification and more stable properties than undigested HA.The flocculation limit of two kinds of HA are 20.0 mmol/L and 38.8 mmol/L respectively and compared with the mineral source HA, sludge HA has better electrolyte stability and greater resistance to hard water.Thermal decomposition behavior and dynamics law of digested HA was researched using thermal gravimetric analysis（TG-DTG）.Non-isothermal data of thermal decomposition processwas analyzed by using Flynn-Wall-Ozawa integration method、Kissinger maximum rate method and ?atava-?estákintegral method. The results showed that the thermal decomposition of sludge HA occurs mainly in the 473.15⁷73.15 Kand is divided into two stages.The mechanism function of the first stage of thermal decomposition process meets Avrami-Erofeev（n=3）equations and its integral expression is: G（α） =-ln（1- α）; the apparent activation energy E=168.718 kJ/mol, pre-exponential factor A = 1.770 × 10 s.The mechanism function of the second stage of thermal decomposition process meets Avrami-Erofeev（n=4）equations and its integral expression is: G（α） =-ln（1- α）; the apparent activation energy E = 136.446kJ/mol, pre-exponential factor A = 4.295 × 10 s. At the same time, the ?G≠、?H≠ and ?S≠ of two-stage of thermal decomposition process were also calculated respectively, which provides a theoretical basis for further study of sludge HA.Static adsorption experiments studied adsorbent dosage、initial concentrationof Cu²⁺、 pH and temperature on the adsorption properties systematically and its results obtained thatthe optimum conditions of sludge HA for Cu²⁺ adsorption were as follows:adsorbent dosage was 10mg、pH=4.0、the adsorption temperature was 298K、 theequilibrium time of adsorption process was 40⁵0min. The results of adsorption kinetics showed thatadsorption process of sludge HA for Cu²⁺follows the pesudo-second-order kinetic model and its fit factor is greater than 0.99. With the initial concentration of Cu²⁺increasing, equilibrium adsorption capacity increases and the time to reach adsorption equilibrium increases, while the value of adsorption rate constant K decreases. The results of adsorption thermodynamic showed thatadsorption process of sludge HA for Cu²⁺conforms Freundlich isothermal adsorption mode and the ?G0、?H0 of process are less than zero,while ?S0is greater than zero, which showsthe adsorption process of sludge HA for Cu²⁺is spontaneous、 exothermic and increased of entropy and low temperature contributes adsorption reaction.