有机物对鸟粪石结晶法回收污水中磷的影响

以实验室模拟污水探究典型有机物海藻酸钠(SA)、牛血清白蛋白(BSA)、腐殖酸(HA)和葡萄糖对鸟粪石结晶过程和磷回收效果的影响。结果表明,大分子有机物腐殖酸、海藻酸钠、牛血清白蛋白均使鸟粪石平衡条件溶度积PSeq增大、磷回收率下降、鸟粪石纯度降低;小分子有机物葡萄糖对磷回收影响相对较小;4种有机物均造成晶体晶形发生变化。相关性分析表明,在有机物存在下,鸟粪石结晶法的磷回收率与平衡条件溶度积PSeq、鸟粪石晶体纯度间相关性显著,其中腐殖酸存在下相关性最显著。建议在采用鸟粪石法回收污水中的磷时采取措施降低大分子有机物的含量,从而提高鸟粪石结晶法的磷回收率。     

污水处理系统中鸟粪石结垢的控制技术

在城市污水处理厂内,特别是采用生物法去除营养物质的污水处理厂内,如果不采取有效措施控制鸟粪石结垢的产生,将会引起严重的运行和管理问题.重点讨论了鸟粪石结垢的防范措施,包括:改进污水污泥处理工艺、调节污水污泥的pH、降低鸟粪石生成组分浓度、回收鸟粪石沉淀、污水污泥处理设备材料改性等.这些方法各有特点,应根据实际需要相互结合使用.     

污水强化除磷工艺的现状与未来

对强化生物除磷工艺的基本概念、外加碳源的作用、脱氮除磷的关系、环境影响参数进行了阐述,并介绍了聚磷菌菌群研究的最新进展。最后探讨了如何通过生产鸟粪石(MAP)实现磷元素回收,并围绕污水除磷和回收磷这一课题,提出了研究方向。     

除磷系统剩余污泥中营养元素的快速释放及回收

除磷系统的剩余污泥在浓缩、储存及后续的处理过程中均可能引起磷的释放,释放的磷往往导致正在运行的污水处理厂的磷负荷超标,最终引起出水磷的不稳定排放。针对此问题,在分析生物除磷系统剩余污泥化学特性的基础上,探讨除磷剩余污泥中营养元素的快速释放条件及磷回收效果。采用两个平行反应器,其中一个作为控制反应器,另一个添加表面活性剂十二烷基硫酸钠(SDS),在中温厌氧条件下对剩余污泥进行水解,并对水解产物中的营养元素在室温、pH值为9.5、搅拌转速为400 r/min的条件下进行鸟粪石回收。结果表明:生物除磷系统的剩余污泥具有磷含量高、磷释放快速、氮释放缓慢的特点;添加SDS不仅可以促进污泥水解过程中磷和氮的释放,而且对回收鸟粪石有积极作用;综合考虑水解产物中的氮、磷浓度及其比值和水解的时间成本,建议快速水解条件为添加SDS且水解24 h。     

活性污泥促进尿液水解回收鸟粪石研究

为了回收利用尿液和活性污泥中的氮、磷等营养物,首先对尿液中尿素的水解特性进行了监测,对脲酶和活性污泥促进尿素水解的效果进行了研究,发现当脲酶和活性污泥的投加量分别为4.0 mg/L和3.73 g/L时,可使尿液中尿素在2 d内完全水解。对两种方法水解后的尿液开展了以鸟粪石形式回收氮、磷的试验,发现当以Mg/P值(物质的量之比)=1.4投加镁源时可有效回收尿液中的磷,回收率达到99%。对所得沉淀物利用XRD技术和化学元素分析方法进行了检测,发现两种沉淀物中鸟粪石含量在95%左右,纯度均较高。利用活性污泥促进尿液水解并以鸟粪石形式回收氮、磷等营养物可同时作为剩余污泥处置的一种方法。     

从部分水解尿液中同步回收磷资源与电能

部分水解尿液获取方便,而鸟粪石是一种优质的含磷缓释肥,具有较高的经济价值,故以部分水解尿液为研究对象,试图在镁空气燃料电池平台上实现高纯度鸟粪石回收并保留尿液中的大部分尿素。尿液水解度理论计算和磷回收实验的结果共同表明,10%的尿液水解度能够提供足够的铵盐、碱度和缓冲能力,有利于鸟粪石沉淀的生成。镁空气燃料电池经过60 min的反应后,收集到的沉淀产物中鸟粪石(包括钾型鸟粪石)占比为94.92%,此时对尿液中PO₄^3--P的去除率可以达到95.86%,尿液中95.74%的初始尿素得以保留,并且每处理1 m³的尿液能够同时回收0.044kW·h的电能。因此,部分水解尿液可在镁空气燃料电池中实现高纯度鸟粪石沉淀和电能的同步回收。     

电化学沉淀/复合黏土吸附法回收黄水中的营养盐

为了回收黄水中的氮、磷营养盐,构建电化学鸟粪石沉淀反应装置,试验结果表明,当电流密度为2.5 mA/cm^2时,磷回收速率及总回收率都为最高,反应4 h时磷回收率达到97.2%,沉淀产物中鸟粪石晶体的纯度为95.7%;氨氮去除率随电流密度的升高而增加,但电化学沉淀法对氨氮的最大去除率仅为21.6%。利用改性凹凸棒-膨润土复合黏土对电化学沉淀后黄水中的氨氮进行吸附,发现其对氨氮的吸附过程更符合拟二级动力学模型,对氨氮的平衡吸附量可达到15.30 mg/g。扫描电子能谱分散显微镜(SEM-EDS)分析表明,从实际黄水中回收的产物多为棱柱状晶体,晶体表面杂质较多,且含有一定量的钾型鸟粪石。     

基于生物营养盐去除工艺所产污泥的处理对策

青岛市两座采用生物营养盐去除工艺的污水处理厂的运行实践表明,初沉污泥和剩余污泥应尽可能在好氧状态下处理,以避免污泥反硝化上浮、磷酸盐和氨氮的厌氧释放以及由此带来的鸟粪石结垢问题.在生物营养盐去除技术背景下,采用厌氧消化进行污泥稳定的污水处理厂,可以利用"有控制的鸟粪石结晶析出技术"来解决鸟粪石结垢问题;如污泥可以土地利用,宜采用好氧堆肥技术对污泥进行稳定.传统活性污泥法污水厂升级时不但要增加营养盐去除措施,还要考虑到对污泥处理系统进行相应的改造.     

套筒式反应器处理实际污泥水的试验研究

采用曝气吹脱提高碱度法促进鸟粪石在套筒式反应器中结晶以去除实际污泥水中的氮和磷,分析了其效果及存在的问题。连续188 d的运行结果表明,在气水比为30∶1条件下套筒式反应器可同步去除实际污泥水中的氮和磷,但去除效果有限,对NH+4-N和PO3-4-P的平均去除率分别为26.8%和55.7%,且其去除率呈现逆向的变化趋势。其原因在于套筒式反应器中存在大量的悬浮和附着态氨氧化菌(AOB)。尽管如此,采用该反应器仍可从每吨污泥水中回收232g纯度为92%的鸟粪石,因此可在一定程度上达到回收资源的目的。     

城市污水厂侧路回收磷技术研究与工程示范

针对污水厂生物除磷效率不高,普遍采用生物除磷辅以化学除磷的方式,研究采用二沉池污泥侧路厌氧释磷,释磷污泥重新回到曝气池,释磷后的上清液进行磷回收,不仅提高了生物除磷效率,同时回收了宝贵的磷资源。分别考察了释磷时间、p H值、反应时间、物料配比等因素对磷回收的影响,结果表明,厌氧释磷的最佳停留时间为4 h,回收磷酸铵镁的最佳药剂组合为Mg Cl2和氨水,物料的最佳配比n(N)∶n(Mg)∶n(P)=5∶1.6∶1,最佳p H值=10,最佳搅拌速率为400 r/min。在太原市2×104m3/d的开发区污水处理厂建立了侧路回收磷系统,通过对所得沉淀产物进行电镜扫描及能谱分析,可知斜方型晶体为目标产物鸟粪石,产物中夹杂无明显晶形的未知物质;示范工程的生物除磷效率提高了20%,回收磷酸铵镁量为400 kg/d。     

The behaviour of pharmaceuticals and heavy metals during struvite precipitation in urine

Separating urine from wastewater at the source reduces the costs of extensive wastewater treatment. Recovering the nutrients from urine and reusing them for agricultural purposes adds resource saving to the benefits. Phosphate can be recovered in the form of struvite (magnesium ammonium phosphate). In this paper, the behaviour of pharmaceuticals and heavy metals during the precipitation of struvite in urine is studied.When precipitating struvite in urine spiked with hormones and non-ionic, acidic and basic pharmaceuticals, the hormones and pharmaceuticals remain in solution for more than 98%.For heavy metals, initial experiments were performed to study metal solubility in urine. Solubility is shown to be affected by the chemical conditions of stored and therefore hydrolysed urine. Thermodynamic modelling reveals low or very low equilibrium solute concentrations for cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), nickel (Ni) and lead (Pb). Experiments confirmed Cd, Cu and Pb carbonate and hydroxide precipitation upon metal addition in stored urine with a reaction half-life of ca. 7 days.For all metals considered, the maximum specific metal concentrations per gram phosphate or nitrogen showed to be typically several orders of magnitudes lower in urine than in commercially available fertilizers and manure. Heavy metals in struvite precipitated from normal stored urine could not be detected.Phosphate recovery from urine over struvite precipitation is shown to render a product free from most organic micropollutants and containing only a fraction of the already low amounts of heavy metals in urine.     

Phosphorus recovery by struvite crystallization in WWTPs: Influence of the sludge treatment line operation

Phosphorus recovery by struvite (MgNH₄PO₄·6H₂O) crystallization is one of the most widely recommended technologies for treating sludge digester liquors especially in wastewater treatments plants (WWTP) with enhanced biological phosphorus removal (EBPR). In this paper, phosphorus recovery by struvite crystallization is assessed using the rejected liquors resulting from four different operational strategies of the sludge treatment line. Phosphorus precipitation and recovery efficiencies of between 80-90% and 70-85%, respectively, were achieved in the four experiments. The precipitates formed were mainly struvite, followed by amorphous calcium phosphate and, in some experiments, by calcite. The highest global phosphorus recovery taking into account both the sludge line and the crystallizer was achieved when mixed thickening and high elutriation were carried out (8.4 gP/kg treated sludge). However, low struvite content was obtained in the crystallizer with this operation scheme due to the high calcium content in the elutriation stream. Therefore, if the final purpose is to obtain struvite, the reduction of the elutriation flowrate is widely recommended in the case of high water hardness.     

Struvite formation,control and recovery

Recent legislation on the removal of nutrients from wastewater has led to a number of operation problems with struvite scaling. Struvite is MgNH4PO4 x 6H2O and this paper reviews the formation, control and recovery of struvite from primarily municipal wastewater and other waste streams. Treatment options for control and technologies for recovery are discussed.     

Agglomeration of struvite crystals

Struvite crystallisation is widely studied as a way to remove phosphorus from wastewater effluents and simultaneously generates a valuable product for the fertiliser industry. However, to date, some crystallisation processes experimented at either pilot/or full scale face problems linked to the formation of fines. This paper presents results on the investigation of struvite agglomerative properties and the possible application of coagulants and/or flocculants to remove fines. Coagulants investigated were hydrolysing metals salts (Al(3+) and Fe(3+)), calcium compounds and a cationic polymer, polydiallyldimethylammoniumchloride (polyDADMAC). The effects of a natural flocculant (alginate) have also been tested. Results demonstrated that destabilisation of struvite particles by chemical addition was feasible and identified polyDADMAC as a good option for the agglomeration of struvite particles. However, optimisation of its dosage under typical pH conditions for struvite formation showed floc formation to be very pH sensitive.     

The role of the microbial stringent response in excess intracellular accumulation of phosphorous in mixed consortia fed synthetic wastewater

Four bench-scale sequencing batch reactors (SBRs) seeded with activated sludge were operated under either fully oxic or anoxic/oxic conditions and fed synthetic wastewater containing either peptone or acetate. The function of each reactor was assessed through the measure of (i) soluble chemical oxygen demand, orthophosphate, ammonia, and nitrate; and (ii) biomass concentrations of phosphorus, polyhydroxyalkanoate, guanosine tetraphosphate, adenosine monophosphate, adenosine diphosphate, and adenosine triphosphate. In all four reactors, the biomass concentration of phosphorous was correlated statistically with the biomass concentration of ppGpp. The microbial consortia in all four reactors removed an appreciable quantity of phosphorous from solution (67-99%), and the net quantity of phosphorous removed from solution corresponded to the net increase in the biomass concentration of phosphorous. Hence, the microbial stringent response (MSR) was associated with excess intracellular accumulation of phosphorous in mixed microbial consortia fed synthetic wastewater. With recognition of the potential role of the MSR in the removal of soluble phosphorous from wastewater, additional research may lead to further optimization of treatment technologies and the development of new treatment systems for the biological removal of phosphorus from wastewater.     

铝盐深度除磷实验研究

研究了化学除磷常用铝盐单独投加和铝盐与PAM协同作用的除磷效果,并确定了铝盐除磷的最佳反应条件,研究表明,铝盐具有良好的除磷效果,对废水中磷的去除率较高,PAM则能显著提高铝盐的除磷效果。     

Enhancing anaerobic digestibility and phosphorus recovery of dairy manure through microwave-based thermochemical pretreatment

Anaerobic digestion and struvite precipitation are two effective ways of treating dairy manure for recovering biogas and phosphorus. Anaerobic digestion of dairy manure is commonly limited by slow fiber degradation, while struvite precipitation is limited by the availability of orthophosphate. The aim of this work is to study the possibility of using microwave-based thermochemical pretreatment to simultaneously enhance manure anaerobic digestibility (through fiber degradation) and struvite precipitation (through phosphorus solubilization). Microwave heating combined with different chemicals (NaOH, CaO, H₂SO₄, or HCl) enhanced solubilization of manure and degradation of glucan/xylan in dairy manure. However, sulfuric acid-based pretreatment resulted in a low anaerobic digestibility, probably due to the sulfur inhibition and Maillard side reaction. The pretreatments released 20-40% soluble phosphorus and 9-14% ammonium. However, CaO-based pretreatment resulted in lower orthophosphate releases and struvite precipitation efficiency as calcium interferes with phosphate to form calcium phosphate. Collectively, microwave heating combined with NaOH or HCl led to a high anaerobic digestibility and phosphorus recovery. Using these two chemicals, the performance of microwave- and conventional-heating in thermochemical pretreatment was further compared. The microwave heating resulted in a better performance in terms of COD solubilization, glucan/xylan reduction, phosphorus solubilization and anaerobic digestibility. Lastly, temperature and heating time used in microwave treatment were optimized. The optimal values of temperature and heating time were 147 °C and 25.3 min for methane production, and 135 °C and 26 min for orthophosphate release, respectively.