【作者】 苏高强；

【导师】 彭永臻；

【作者基本信息】 北京工业大学 ， 环境工程， 2013， 博士

【摘要】 氮和磷元素的超标是引起水体富营养化问题的主要因素，因此防止水体富营养化的主要措施是将氮磷从污水中去除。活性污泥法是国内外污水厂处理含氮磷污水广泛采用的工艺，在生物脱氮除磷的过程中往往需要较易被利用的碳源，如短链挥发性脂肪酸（Short Chain Volatile FattyAcids, SCFAs），然而生活污水中往往存在碳源不足的问题。同时，在采用生物活性污泥法工艺的污水厂中会有大量的剩余污泥产生，剩余污泥的处理与处置成为污水厂另外一个亟待解决的重要问题。因此，有必要需找出一种既能从污水厂内部开发碳源，又能实现污泥减量的方法。碱性环境中，剩余污泥在发酵过程中能产生大量的SCFAs，并且污泥减量的速率和中性以及酸性条件下相比能得到大幅度提升，因此剩余污泥碱性发酵能解决上述两个问题。虽然研究者们已对剩余污泥碱性发酵的影响因素、机理和微生物学进行了研究，但还存在着何种碱和污泥浓度最佳，如何进一步提升剩余污泥碱性发酵的产酸量，如何改善碱性发酵污泥的脱水性能，如何以较低的成本回收剩余污泥中的碳源和氮磷元素等问题。本研究以剩余污泥作为研究对象，采用批式试验装置，针对以上问题提出了解决办法。针对污泥碱性发酵过程中最佳碱和最佳污泥浓度的选择，考察了碱的类型以及污泥浓度对剩余污泥碱性发酵的影响。碱的类型（KOH、NaOH、Ca（OH）2和Na₂CO₃）对剩余污泥的水解、产酸以及脱水性能均有重要的影响。剩余污泥的水解能力在Na₂CO₃条件下最佳，产酸能力在NaOH条件下最佳但脱水性能在该条件下最差，脱水性能在Ca（OH）2条件下最佳但水解和产酸在该条件下最差。温度15℃和35℃条件下，剩余污泥的污泥浓度（挥发性悬浮固体浓度（VolatileSuspended Solid，VSS）为1.708、3.146、5.124、6.832、8.540和11.049g/L）对碱性条件下剩余污泥的水解影响不大，但高浓度和低浓度条件下均不利于污泥产酸，最佳的产酸污泥浓度为8.540g/L。针对如何提高剩余污泥碱性发酵过程中的产酸量，考察了污泥发酵方式、镁粉的投加对剩余污泥碱性条件下水解和产酸的影响，以及污泥碱性发酵过程中氢氧根和金属离子的作用。首先考察了pH值对混合污泥水解酸化的影响，而后对比考察了剩余污泥和初沉污泥单独发酵以及混合发酵时的水解和产酸能力。结果表明pH值对混合污泥、剩余污泥以及初沉污泥的水解酸化的影响相似，这三种污泥均在碱性环境中有较高的水解和产酸能力，20²2℃条件下产酸均在pH值为10时达到最大。同时将剩余污泥和初沉污泥混合后不会对污泥的产酸产生抑制作用，反而会有一定的促进作用。考察了镁粉投加对剩余污泥碱性发酵的影响，结果表明镁粉投加不会对剩余污泥的溶解产生影响，但会增强蛋白酶的活性，从而提高污泥的产酸量。最佳的镁粉投加量为0.01g/g（TSS）。氢氧化钠对剩余污泥水解和产酸的促进作用一部分是靠氢氧根，一部分是靠钠离子。钠离子能够提高剩余污泥的溶解率，增加蛋白质和多糖的溶出量，同时可以抑制产甲烷生物的生长，从而提高剩余污泥的产酸量。剩余污泥发酵后回收发酵液作为碳源，需要将发酵液和污泥进行分离，进一步考察了使用NaOH、Ca（OH）₂以及两者的混合液控制pH为10时对剩余污泥水解产酸以及污泥脱水的影响。在NaOH条件下具有较高的产酸量，但由于发酵液中存在高浓度的钠离子，污泥的脱水性能差。剩余污泥在Ca（OH）2条件下污泥的脱水性能好，但由于发酵液中存在高浓度的钙离子，抑制了蛋白质的水解，导致污泥产酸量较低。在使用两者的混合液控制pH值时，降低了发酵液中钠离子的浓度，而且由于氢氧化钙的加入改善了污泥的脱水性能。且氢氧化钙释放的钙离子在发酵过程中可以和氢氧化钠以及二氧化碳反应生成沉淀，从而使得钙离子的浓度较低，对蛋白质的抑制作用不明显。因此使用NaOH和Ca（OH）₂的混合液控制剩余污泥pH值不仅污泥的产酸量较高，而且污泥的脱水性能也较好。剩余污泥在发酵过程中会释放出大量的氨氮和正磷酸盐，影响发酵液作为碳源进行脱氮除磷，因此将发酵液和污泥分离后，需要将发酵液中的氨氮和正磷酸盐进一步回收。因此考察了使用氢氧化钠，磷酸钠以及两者混合液控制pH值对剩余污泥水解产酸以及使用鸟粪石沉淀法回收氮磷的影响。发现三种条件下污泥的水解和产酸能力相当，但混合碱条件下发酵液中P/N（正磷酸盐和氨氮的比值）摩尔比比在0.9¹.4之间，最适合回收发酵液中的氨氮和正磷酸盐。且混合碱条件下能节省控制污泥pH所需的氢氧化钠以及回收氨氮和正磷酸盐时调节pH所需的盐酸的量，因此联合使用氢氧化钠和磷酸钠可以减少回收成本。更多还原

【Abstract】 Overload of nitrogen and phosphorus in the waterbody is the main reason foreutrophication, an essential strategy for controlling eutrophication is to removenitrogen and phosphorus from wastewater before discharge. Activated sludge processis widely used for nitrogen and phosphorus removal home and abroad in the wastewater treatment plants （WWTPs）. Readily degradable carbon sources, such as shortchain fatty acids （SCFAs） are need in the biological nitrogen and phosphorus removalprocess. However, carbon sources are often not adequate in the influent.Simultaneously, a large amount of waste activated sludge production in the activatedsludge process became another problem that should be solved urgently. Therefore,technology which both can produce carbon sources in the WWTPs and realize sludgereduction is needed.Under alkaline condition, abundant VFA could be produced in the fermentationprocess of waste activated sludge （WAS）, and the reduction rate of sludge could beenhanced compared with those under neutral and acid condition, hence fermentingWAS under alkaline condition can solve the two problems mentioned above. Theinfluence factors, mechanisms and microorganisms of WAS alkaline fermentationprocess had been studied by researchers. However, which alkali and sludgeconcentration are the best, how to further improve the acid production of the WASalkaline fermentation process, how to improve the sludge dewaterability of WAS inthe alkaline fermentation process and how to recycle carbon source, nitrogen andphosphorus with a low cost still need to be discussed. A series of batch tests weredone by treating WAS under alkaline conditions to give answers to those problems.Effects of alkali types and sludge concentrations on WAS alkaline fermentationwere investigated to indentify which alkali and sludge concentration are the best.Alkali types （KOH、NaOH、Ca（OH）2and Na₂CO₃） influenced significantly on WAShydrolysis, acidification and dewaterability. WAS hydrolysis was the best underNa₂CO₃condition, and sludge acidification was the best but the sludge dewaterabilityis the worst under NaOH condition, the sludge dewaterability is the best but sludgeacidification was the worst under Ca（OH）2condition. Under15℃and35℃, sludgeconcentrations （volatile suspended sludge concentrations were1.708、3.146、5.124、6.832、8.540and11.049g/L, respectively） insignificantly influenced sludge hydrolysis, but high and low sludge concentrations disadvantaged VFA production of WAS, andthe best sludge concentration for acid production was8.540g/L.Effects of fermentation mode, adding magnesium powder on sludge hydrolysisand acidification in WAS alkaline fermentation process, and the effects of hydroxyland metal ions in the alkaline fermentation process were investigated to furtherimprove the acid production of the WAS alkaline fermentation process. The effects ofpH values on mixed sludge （mixture of primary sludge and waste activated sludge）hydrolysis and acidification were firstly studied, then hydrolysis and acidificationabilities of separately-fermented sludge and co-fermented sludge were compared. Theresults showed that the effects of pH on hydrolysis and acidification of primary sludge,waste activated sludge and mixed sludge were similar, alkaline conditions benefitedthe hydrolysis and acidification of the three types of sludge, and the best pH value foracid production were all at pH10under20²2℃. Compared withseparately-fermenting primary sludge and waste activated sludge, co-fermenting themdidn’t impede acid production but could improve acid production. Adding magnesiumpowder didn’t affect WAS solubilisation, but can enhance the activity of protease andimprove VFA production, and the optimal addition was0.01g/g （TSS）.Theenhancement of NaOH on solubilisation and acidification of WAS were mainly due tohydroxyl, and partly due to sodium ion. NaCl improved the solubilisation of WAS,and sludge solubilisation efficiencies, protein and carbohydrate release all increasedwith the dosage of NaCl, NaCl also could inhibit the growth of methanogens. Theimprovement of sludge solubilisation and inhibit of the growth of methanogens byNaCl enhanced VFA production of WAS.Fermentation liquid should be separated from fermented sludge afterfermentation to be used as carbon source for nitrogen and phosphorus removal.Hydrolysis, acidification and dewaterability of waste activated sludge （WAS） wereinvestigated at pH10controlled by the addition of NaOH, Ca（OH）2or their mixturesat various ratios. Under the solo NaOH condition, VFA production was high. However,the sludge dewaterability was negatively affected due to a large release of Na+fromNaOH. Under the Ca（OH）2condition, the sludge dewaterability was good due to theaddition of Ca（OH）2, but the VFA production was low. Because Ca²⁺was releasedthrough neutralizing reaction between VFA and Ca（OH）2, and a high concentration ofCa²⁺inhibited the hydrolysis of protein, so only a small quantity of VFA could beproduced. Under the mixed alkaline condition, the concentrations of Na+in the fermentation liquid decreased and Ca（OH）2was provided simultaneously, both ofwhich could improve sludge dewaterability. Ca²⁺released by Ca（OH）2could beprecipitated by reacting with NaOH and CO2, and little amount of Ca²⁺could bereleased from Ca（OH）2. The low concentration of Ca²⁺insignificantly inhibited thehydrolysis of protein, thus allowing a high level of VFA production. Thus, treatingWAS with mixtures of NaOH and Ca（OH）2could enable both high VFA productionand good sludge dewaterability.A significant amount of NH₄⁺-N and PO₄^3--P was released into the fermentationliquid in the fermentation process of WAS, which could impede fermentation liquid tobe used as carbon source for nitrogen and phosphorus removal. NH4+-N and PO43--Pshould be removed firstly before the fermentation liquid was used for nitrogen andphosphorus removal. The hydrolysis and acidification of waste activated sludge wereinvestigated under three types of alkaline conditions, which were NaOH, Na3PO4andcombination of NaOH and Na3PO4. Then the recovery of ammonia and phosphorus inthe form of struvite from the three types of alkaline fermentation liquid was conducted.The results show that the hydrolysis and acidification abilities of WAS under the threetypes of alkaline conditions were similar. However, the molar ratio of phosphorus andammonia in the sludge fermentation liquid was in the range of0.9¹.4under themixed alkaline condition, which was the most suitable for ammonia and phosphorusrecovery in the form of struvite. Under the mixed alkaline condition, the dosage ofNaOH in the alkaline fermentation process could be saved, and the dosage of HCl alsocould be saved in the nitrogen and phosphorus recovery process, so combined use ofNaOH and Na3PO4could save the cost for recycling carbon source, nitrogen andphosphorus.更多还原