Nitrogen recovery by urea hydrolysis and struvite precipitation from anthropogenic urine.

Human urine is a source of nutrients and has a significant potential for recycle of nitrogen. Recently, much research focused on separate collection and treatment of human urine. Recovery of nutrients from human urine requires hydrolysis of urea into ammonia and subsequent removal of ammonia and sometimes phosphorus. This study attempted to evaluate urea hydrolysis of human urine in both untreated fresh samples and urease added urine samples. Recovery of nutrients by struvite precipitation on pre-hydrolysed samples was also assessed on undiluted and 1:1 diluted samples. Results of urea hydrolysis on untreated urine samples indicated that the process was slow and pH exerted a significant effect on the process. No hydrolysis occurred above pH 10. From pH 2 to 7.5, 25% of urea could be hydrolysed in 30 d. Urease added hydrolysis with the enzyme doses 25-49 mg L(-1) was a rapid process providing complete conversion into ammonia in 1.5 h. Struvite precipitation conducted on enzyme hydrolysed urine sample proved to be an efficient process and ammonia removals up to 95% were obtained. Struvite precipitation also provided 50% organic nitrogen removal.     

Fate of pharmaceuticals and bacteria in stored urine during precipitation and drying of struvite

Experiments were conducted to measure the behaviour of eight pharmaceuticals during urine treatment as part of the project 'SANIRESCH - Sustainable sanitary recycling Eschborn'. Urine was collected from 200 people in a public building via waterless urinals and NoMix toilets. It was then stored at room temperature at different pH values to analyse the extent to which bacteria and pharmaceuticals are eliminated over time. Although a partial elimination of pharmaceuticals could be detected, the storage at defined pH values cannot be advised. As the persons tested used pharmaceuticals with different structures, in different amounts and at varying intervals, this method of treatment is insufficient for removing them from urine. Precipitating the urine with MgO, washing it with saturated struvite solution and drying it at 30 °C will result in a free-flowing granular powder of struvite (NH(4)MgPO(4)·6H(2)O) that is free of pharmaceuticals and pathogens and can be used as fertiliser and a source of nitrogen, magnesium and phosphorus.     

Importance and measurement of decay rate when assessing nitrification kinetics.

Nitrification kinetics are important for process design, optimization and capacity rating of activated sludge wastewater treatment plants. Assessment of nitrification behaviour historically has focused on measuring the nitrifier maximum specific growth rate, micro(AUT). Very little attention has been directed at the of nitrifier organism rate has been assumed negligible. However, incorrect assessment of decay rate leads to errors in the micro(AUT) estimate; the magnitude of the error depends on the micro(AUT) measurement method employed. This paper illustrates why decay rate is important when measuring micro(AUT), and that the decay rate is significant. The paper also explains why measurement methods for nitrifier decay may have underestimated the decay rate. Results from an experiment incorporating improvements to previously suggested methods and data analysis are presented.     

Influence of physico-chemical treatment on the subsequent biological process treating paper industry wastewater

The present paper presents the main results of the biodegradation study of paper industry wastewater through physico-chemical treatment. Indeed, around 60% of chemical oxygen demand (COD) removal can be achieved by electroflocculation treatment. Furthermore, a removal efficiency of the COD of almost 91% has been obtained by biological treatment, with activated amount of sludge for 24 h of culture. Concerning the physico-chemical pre-treatment of the untreated, filtered and electroflocculated rejection effluents, it has been investigated through the degradation curve of COD studies.     

Treatment of spent brine from a nitrate exchange process using combined biological denitrification and sulfate precipitation.

A combined biological denitrification and sulfate precipitation process was developed to treat and reuse the spent brine produced by a nitrate exchange system. Although the spent brine contained a relatively high salt concentration, more than 80% of NO3(-)-N fed into the denitrification reactors was removed at a nitrate-N loading rate of 2.2 g NO3(-)-N/l x day, regardless of the presence or absence of sulfate up to 8,000 mg/l. Sulfate present in the spent brine was successfully removed by the addition of BaCl2 and the settling velocity of BaSO4 suspension was remarkably enhanced by FeCl3 coagulation. Since most of the chloride consumed in regenerating the exhausted resins was replaced during chemical treatment with BaCl2 and FeCl3, it was possible to reuse the treated spent brine as a regenerant after compensating for the small amount of unreplaced NaCl.     

TOC与IC对厌氧氨氧化反应的影响研究

在将厌氧氨氧化技术成功应用于城市污水深度处理后,进一步考察了废水中碳源类型对厌氧氨氧化反应的影响。结果显示:进水中无机碳浓度的提高,将利于厌氧氨氧化菌的生长,但当其超过一定浓度时(IC>55.77mg/L),厌氧氨氧化反应速率将会下降;有机碳的存在将会降低厌氧氨氧化菌的活性,浓度越高其抑制作用越强,短时间内该抑制作用是可逆的;当废水中有机碳浓度较高时,为取得良好的处理效果,必须提高进水中NO2-—N/NH3—N。虽然厌氧氨氧化技术是在处理高氨废水时发现的,但就脱氮速率而言,它更适用于处理低氨废水。     

水工混凝土配合比参数的分析与确定

本文针对混凝土配合比方案设计中水胶比、单位用水量、外加剂与粉煤灰掺量等4个参数对混凝土配合比的影响进行了分析,以工程实例进行了说明,提出合理经济地确定4个参数的方法,为混凝土配合比优化设计提供参考.     

LEED节水条款实现方法与相关参数确定

结合在LEED NC认证中具体工程实践,参考国内外相关标准和规范,分析节水相关条款内容并阐述具体实现方法.在实现认证要求的同时,根据具体应用环境,探讨了雨水调蓄池容积确定的思路.同时,也对绿色建筑认证中标准方法的制定提供一些启示和探索.     

MSBR工艺控制参数总结与分析

介绍了MSBR工艺的原理,并通过分析近两年的工艺运行情况,总结得出该工艺的主要污泥性能参数。通过研究工艺控制参数与出水水质的关系得出:工艺有机负荷宜控制在0.2～0.4kgBOD5/(kgMLVSS.d),泥龄在10～20d。此外还分析了MSBR工艺中回流量和排泥时间、DO等主要控制点的调整依据和调整措施,为该工艺在其他污水处理厂的应用提供借鉴。     

过程降水与旱地土壤水渗透规律分析

根据多年实测土壤含水量资料,分析本地区土壤水季节性的变化规律。以2003年夏秋季发生的大范围降水过程分析旱地农田土壤水增长和消退过程,确定不同质地土壤的最大田间持水量指标,研究影响旱地土壤水变化的因素及特性,科学判别旱涝程度,为农业生产、防汛抗旱、生态环境治理和水资源可持续利用提供依据。     

Solutions to a combined problem of excessive hydrogen sulfide in biogas and struvite scaling.

The Woodman Point Wastewater Treatment Plant (WWTP) in Western Australia has experienced two separate problems causing avoidable maintenance costs: the build-up of massive struvite (MgNH4PO4. 6H2O) scaling downstream of the anaerobic digester and the formation of hydrogen sulfide (H2S) levels in the digester gas to levels that compromised gas engine operation and caused high operating costs on the gas scrubber. As both problems hang together with a chemical imbalance in the anaerobic digester, we decided to investigate whether both problems could be (feasibly and economically) addressed by a common solution (such as dosing of iron solutions to precipitate both sulfide and phosphate), or by using separate approaches. Laboratory results showed that, the hydrogen sulfide emission in digesters could be effectively and economically controlled by the addition of iron dosing. Slightly higher than the theoretical value of 1.5 mol of FeCl3 was required to precipitate 1 mol of dissolved sulfide inside the digester. Due to the high concentration of PO4(3-) in the digested sludge liquor, significantly higher iron is required for struvite precipitation. Iron dosing did not appear an economic solution for struvite control via iron phosphate formation. By taking advantage of the natural tendency of struvite formation in the digester liquid, it is possible to reduce the risk of struvite precipitation in and around the sludge-dewatering centrifuge by increasing the pH to precipitate struvite out before passing through the centrifuge. However, as the Mg2+/PO4(3-) molar ratio in digested sludge was low, by increasing the pH alone (using NaOH) the precipitation of PO4(3-) was limited by the amount of cations (Ca2+ and Mg2+) available in the sludge. Although this would reduce struvite precipitation in the centrifuge, it could not significantly reduce PO4(3-) recycling back to the plant. For long-term operation, maximum PO4(3-) reduction should be the ultimate aim to minimise PO4(3-) accumulation in the plant. Magnesium hydroxide liquid (MHL) was found to be the most cost-effective chemical to achieve this goal. It enhanced struvite precipitation from both, digested sludge and centrate to the point where more than 95% PO4(3-) reduction in the digested sludge was achieved.     

Effect of organic loading rate on a wastewater treatment process combining moving bed biofilm and membrane reactors.

The effect of moving bed biofilm reactor (MBBR) loading rate on membrane fouling rate was studied in two parallel units combining MBBR and membrane reactor. Hollow fiber membranes with molecular weight cut-off of 30 kD were used. The HRTs of the MBBRs varied from 45 min to 4 h and the COD loading rates ranged from 4.1 to 26.6 g COD m(-2) d(-1). The trans-membrane pressure (TMP) was very sensitive to fluxes for the used membranes and the experiments were carried out at relatively low fluxes (3.3-5.6 l m(-2) h(-1)). Beside the test with the highest flux, there were no consistent differences in fouling rate between the low- and high-rate reactors. Also, the removal efficiencies were quite similar in both systems. The average COD removal efficiencies in the total process were 87% at 3-4 h HRT and 83% at 0.75-1 h HRT. At high loading rates, there was a shift in particle size distribution towards smaller particles in the MBBR effluents. However, 79-81% of the COD was in particles that were separated by membranes, explaining the relatively small differences in the removal efficiencies at different loading rates. The COD fractionation also indicated that the choice of membrane pore size within the range of 30 kD to 0.1 microm has very small effect on the COD removal in the MBBR/membrane process, especially with low-rate MBBRs.     

Identification of the adverse effect of nitrate on the phosphate release rate and improvement of EBPR process models.

The adverse effect of nitrate on the phosphate release rate in the anaerobic phase was observed and was hardly explainable with conventional EBPR process models. Four possible mechanisms were proposed including substrate competition, reduced fermentation, parallel reaction and sequential reaction. Batch experiments were designed and conducted to identify the dominant mechanism. Results showed that the sequential reaction was the only possible mechanism where only denitrification occurred if any nitrate existed in the anaerobic phase. Then the phosphate release following after the nitrate was completely removed. Nitrate inhibition effect was added into the PHA storage rate to incorporate the sequential reaction in the conventional ASM3 plus EAWAG bio-P module (ASM3 + P). Nitrate inhibition coefficient, K(I,NO,PAO) was found to be as low as 0.05 mg/L. This correlated well with experimental observation where no also meant that the anaerobic compartment of a continuous flow reactor could be seriously affected by the residual nitrate contained in the sludge recycle flow. This phenomenon caused overestimation of the phosphate uptake rate and consequently underestimation of PO4(3-) -P concentration. This problem was resolved by incorporation of a nitrate inhibition term in the ASM3 + P for more accurate simulation of the EBPR process.     

用全程曲线拟合法确定承压含水层参数的研究

含水层参数的确定是地下水资源评价、数值模拟、开发利用与保护,以及科学管理的重要基础,抽水试验法是确定含水层参数的主要方法．根据承压含水层抽水试验的泰斯(Theis)公式。运用优化理论,结合计算机技术,提出利用抽水试验数据确定承压含水层参数的全程曲线拟合法．实例研究表明。该方法速度快、精度高、参数求解结果最优,因而在科学研究和生产实践中具有重要的实用价值．     

斜管沉淀池布水均匀性模拟计算与工艺参数分析

水量负荷的增大和水质标准的提高,迫使许多水厂不得不将平流沉淀池改造为斜管沉淀池,然而改造过程中所遇到的斜管布水均匀性问题一直没从理论上得以解决。通过建立包括长宽比、斜管管径、布水区高度等多个影响布水均匀性因素的水力学方程,定量分析了各种因素的影响规律。模拟计算结果表明:沉淀池长宽比(L/B)对均匀布水性影响最大,当L/B接近6时,布水渠末端的斜管流量极小,布水极不均匀;增大布水渠高度和沿池长方向上减小斜管管径有利于提高布水均匀性。据此在L/B较大的平流沉淀池改造工程中可采取由沿宽度方向布水改为沿长度方向,将沉淀池分格改造为多个斜管沉淀池以及斜管管径沿布水方向由小变大等技术措施提高布水均匀性。     

A study of NH3-N and P refixation by struvite formation in hybrid anaerobic reactor.

This research is concerned with the removal of ammonia nitrogen and phosphorus in foodwaste by crystallization. Reductions have been achieved by struvite formation after the addition of magnesium ions (Mg2+). Magnesium ions used in this study were from magnesium salts of MgCl2. The results of our analysis using scanning electron microscopy and energy dispersive X-ray analysis showed that the amount of struvite in precipitated sludge grew enough to be seen with the naked eye (600-700 microm). EDX analysis also showed that the main components of the struvite were magnesium and phosphorus. NH3-N removal efficiency using MgCl2 was 67% while PO4-P removal efficiency was 73%. It was confirmed that nitrogen and phosphorus could be stabilized and removal simultaneously through anaerobic digestion by Mg, NH3 and PO4-P, which were necessary for struvite formation.     

Effects of pre-treatment with magnetic ion exchange resins on coagulation/flocculation process.

A new Magnetic Ion EXchange resin for DOC (Dissolved Organic Carbon) removal (MIEX DOC Resin) has been evaluated as water pre-treatment at the Drinking Water Treatment Plant (DWTP) of Florence in order to reduce the oxidant demand and disinfection by-products (DBPs) formation potential. This pre-treatment leads to several effects on downstream treatment processes. In this experimental study the effects of MIEX pre-treatment on clariflocculation process were evaluated with respect to coagulant demand reduction and characteristics of flocs formed. The analysis was conducted using traditional jar test procedures and a Photometric Dispersion Analyser (PDA2000) which provided continuous information about the aggregation state of particles during the jar tests.For a fixed turbidity goal in clarified water, ion exchange pre-treatment led to coagulant dosage reduction up to 60% and PDA results shown that flocs formed in pre-treated water were bigger and more resistant to shearing effects than those formed by conventional clariflocculation.     

Effects of flux enhancing polymer on the characteristics of sludge in membrane bioreactor process.

A newly developed membrane performance enhancer (MPE) was used to prevent membrane fouling in a membrane bioreactor (MBR) process. It transpired that 1,000 mg/l of MPE reduced polysaccharide levels from 41 mg/I to 21 mg/I on average under the experimental condition. Repeated experiments also confirmed that 50-1,000 mg/l of MPE could reduce membrane fouling significantly and increase the intervals between membrane cleanings. Depending on MPE dosages and experimental conditions, trans-membrane pressure (TMP) increase was suppressed for 20-30 days, while baseline TMP surged within a few days. In addition, MPE allowed MBR operation even at 50,000 mg/l of total solid and reduced permeate COD. However, no evidence of toxicity for sludge was found from respiratory works.     

复合倒置A~2/O工艺优化运行参数研究

结合污水处理厂升级改造开展中试研究,考察水力停留时间(HRT)、污泥龄(SRT)和回流比等运行参数对复合倒置A~2/O工艺处理性能的影响,优化工艺运行参数.试验结果表明,在常温和低温条件下,复合倒置A~2/O工艺所需泥龄较短,当SRT为12 d时,既可保证良好的硝化水平,又可提高除磷效果;当回流比为200%时,可获得良好的同步脱氮除磷效果.     

Impact of hydrodynamics on the precipitation efficiency--application to HARDTAC reactor.

Precipitation of gypsum is studied in a HARDTAC (High-Aspect Ratio, Draft-Tube, Agitated Crystallizer) reactor, which is considered as the core crystallization unit of lots of wastewater treatment systems. Coupling Computational Fluid Dynamics (CFD) and population balance modelling to simulate precipitation can be a useful tool to come to a decision about upstream and downstream units. In the present study, we aim to validate such approach by investigating gypsum precipitation in a HARDTAC pilot unit and comparing experiments results with simulation. Measured nucleation and growth kinetics are used to feed the model. A comparison between experiments and simulations is presented in the case of gypsum precipitation with a given set of operating conditions. Good agreement is obtained for species concentrations, gypsum mass fraction and volumetric mean diameter but some discrepancies still remain between measured and simulated crystal size distribution.