Recovering phosphorus as struvite from the digested swine wastewater with bittern as a magnesium source

Recovering nitrogen and phosphorus through struvite (MgNH4PO4 6H2O) crystallization from swine wastewater has gained increasing interest. However, swine wastewater contains complex compositions, which may hinder the formation of struvite crystal and affect the purity of the precipitates by forming other insoluble minerals. In this work, experiments were carried out to evaluate struvite precipitation in the anaerobically digested swine wastewater, with dosing bittern as a low-cost magnesium source. Exceeded 90% phosphate removal and 23-29% ammonium reduction were obtained. FTIR, XRD and mass balance analysis were combined to analyze the species of precipitated minerals. Results showed that the precipitates were struvite, mixed with amorphous calcium phosphate (ACP) and brucite. The presence of Ca2+ diminished the percentage of struvite and gave rise to ACP formation. Controlling pH below 9.5 and bittern dosage above 1% (w/w) could inhibit ACP precipitation and harvest a highly pure struvite crystal product.     

Ammonium nitrogen removal from slurry-type swine wastewater by pretreatment using struvite crystallization for nitrogen control of anaerobic digestion.

Precipitation of ammonium together with phosphate and magnesium is a possible alternative for lowering the nitrogen content of wastewater. In this study we examine the removal of ammonium nitrogen and phosphorus from slurry-type swine wastewater containing high concentrations of nutrients by the addition of phosphoric acid along with either calcium oxide or magnesium oxide, which leads to the crystallization of insoluble salts such as hydroxyapatite and struvite. The struvite crystallization method showed a high capacity for the removal of nitrogen when magnesium oxide and phosphoric acid were used as the magnesium and phosphate sources, respectively. When it was applied to swine wastewater containing a high concentration of nitrogen, the injection molar ratio of Mg2+:NH4+:PO4(3-) that gave maximum ammonium nitrogen removal was 3.0:1.0:1.5.     

污水处理厂回流液中回收磷酸铵镁的试验研究

用污水处理厂回流液进行磷酸铵镁(MAP)沉淀试验,研究化学沉淀法回收MAP的适宜条件.结果表明,pH为8～11时生成沉淀的主要成分为MAP;当pH为10,药剂配比n(NH+4)∶n(Mg2+)∶n(PO43-)控制在1∶1∶1和1∶1.4∶1时得到的晶体纯度高,前者形成的沉淀量为5.3 g/L,氨氮去除率为90.86%;后者形成的沉淀量为5.74 g/L,氨氮去除率为95.84%.分析表明从回流液中回收MAP可以大幅降低处理成本以及系统的氮磷负荷,还可解决MAP结垢问题,实现资源的再生.     

藻华聚积及污水入流对太湖上下层水体营养盐含量的影响

通过采集太湖水体鲜藻和入湖区混合常见污水,应用再悬浮发生装置,室内模拟有底泥参与的不同藻类聚积和不同CODCr含量污水进入条件下,太湖西北竺山湖区水质上下层水体中SS,NH3-N及PO43-质量浓度的变化过程。分析结果表明:在7 d的常见风浪模拟环境中,无论加入藻类还是加入污水,太湖上下层水体中SS质量浓度均呈下降趋势,表明颗粒物有向水底沉降的可能;水体中的NH3-N和PO43-质量浓度并未因藻量增加而上升,反映出鲜藻此时对水体中的N和P呈吸收作用;污水添加量的增大则使试验水柱中NH3-N和PO43-质量浓度上升,并大致随时间的增加呈逐步上升的趋势。     

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.     

菌藻混合固定化及其对污水的净化实验

对菌藻共固定化系统进行研究,初步确定菌藻共固定化中较佳的污泥包埋量。在同等条件下,固定化菌藻对氮磷的去除效果优于固定化细菌和固定化藻类的去除效果。对氨氮和磷酸盐磷去除能力的48 h实验结果表明,按去除率的大小排列为:固定化菌藻固定化小球藻固定化细菌,固定化菌藻对NH4+-N和PO43--P的去除率分别达到97.09%和88.69%,可见把细菌和藻类共同包埋于同一载体内,在同时去除污水中的氮磷和有机物方面有着更大的优势。     

生物滤池串联工艺处理西洋河淀粉废水

为减少西洋河淀粉废水中大量N、P、CODCr进入洋河水库,加剧水库的富营养化,进行了 生物滤池串联工艺处理西洋河淀粉废水的研究。结果表明:系统对淀粉废水中的氨氮、总氮、总磷、 可溶性总磷、正磷酸盐、CODCr均具有较好的去除效果,去除率可分别达到57．7％、58．7％、66．8％、 65．7％、67．4％、75．2％,且对进水浓度变化具有一定的适应性。     

Impacts of nutrients and related environmental factors on distribution and size structure of Noctiluca scintillans populations of the eutrophic Tha Chin estuary, Thailand

This study aimed to analyze the impacts of nutrients and related aquatic factors on changes in the Noctiluca population of the Tha Chin estuary, a nutrient-rich estuary located in the inner Gulf of Thailand. Field surveys were carried out at 30 stations during November 2009 to August 2010. The results indicated high levels of dissolved inorganic nitrogen (DIN; 13.89-46.99 μmol/L) and PO(4)(3-)-P (0.20-3.05 μmol/L) where the Noctiluca red tide occurred, particularly during the high-loading period. Dense populations were usually found in the outer part of the estuary with comparatively high salinity (25-29 psu). The highest Noctiluca density was 72,333 cells L(-1) and the cell diameters ranged between 360 and 460 μm. Proportions of small-sized cells (P(s); less than 300 μm) varied over time. In this study, P(s) showed a positive correlation with levels of PO(4)(3-)-P, while the total population density was significantly affected by levels of NH(4)(+)-N and DIN (p < 0.05). Overall, PO(4)(3-)-P influenced the development of the Noctiluca red tide, with the limitation of PO(4)(3-)-P levels to below 1 μmol/L suggested for controlling Noctiluca red tide outbreaks at their origin. To support environmental conservation and maintain sustainable production in the estuary, the levels of PO(4)(3-)-P should be considered for the further effective development of water quality standards in estuarine zones.     

Treatment of strong nitrogen swine wastewater in a full-scale sequencing batch reactor.

Treatment of swine wastewater containing strong nitrogen was attempted in a full-scale SBR. The strongest swine wastewater was discharged from a slurry-type barn and called swine-slurry wastewater (SSW). Slightly weaker wastewater was produced from a scraper-type barn and called swine-urine wastewater (SUW). TCOD, NH4+-N and TSS in raw SSW were 23,000-72,000 mg/L, 3,500-6,000 mg/L and 17,000-50,000 mg/L, respectively. A whole cycle of SBR consists of 4 sub-cycles with anoxic period of 1 hr and aerobic period of 3 hr. The maximum loading rates of both digested-SSW and SUW were similar to 0.22 kg NH4+-N/m3/day whereas the maximum loading rates of raw SSW was up to 0.35 TN/m3/day on keeping the effluent quality of 60 TN mg/l. The VFAs portion of SCOD in raw SSW was about more than 60%. The VFAs in SUW and digested-SSW were about 22% and 15%, respectively. NH4+-N and PO4(3-)-P in SSW were removed efficiently compared to those in digested-SSW and DUW because SSW had high a C/N ratio and readily biodegradable organic. High concentration of organic was useful to enhance denitrification and P uptake. Also the amount of external carbon for denitrification was reduced to 5% and 10% of those for digested-SSW and SUW.     

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.     

Treatment of the butadiene washing stream from a synthetic rubber industry and recovery of p-TBC.

Butadiene is marketed containing p-tertbutylcatechol (p-TBC), a polymerization inhibitor that should be removed before butadiene utilization in synthetic rubber production. p-TBC can be removed from butadiene by washing with sodium hydroxide (NaOH) solution, producing a wastewater with pH 14, which contains high amounts of p-TBC, a toxic chemical compound. The aim of this work was to develop a treatment process that could reduce the content of p-TBC from the wastewater. Since p-TBC is very soluble in basic, but not in neutral and acid solutions, acidification tests were performed with phosphoric acid (H3PO4) to precipitate p-TBC. Reaction between NaOH and H3PO4 can result in crystallization of large amounts of salt without p-TBC precipitation. Under selected acidifying conditions p-TBC precipitates and the wastewater COD is highly reduced (> 90/o). Chromatographic determinations showed that the precipitated p-TBC could be recovered with 99% purity.     

Evaluation and thermodynamic calculation of ureolytic magnesium ammonium phosphate precipitation from UASB effluent at pilot scale

The removal of phosphate as magnesium ammonium phosphate (MAP, struvite) has gained a lot of attention. A novel approach using ureolytic MAP crystallization (pH increase by means of bacterial ureases) has been tested on the anaerobic effluent of a potato processing company in a pilot plant and compared with NuReSys(?) technology (pH increase by means of NaOH). The pilot plant showed a high phosphate removal efficiency of 83 ± 7%, resulting in a final effluent concentration of 13 ± 7 mg · L(-1) PO(4)-P. Calculating the evolution of the saturation index (SI) as a function of the remaining concentrations of Mg(2+), PO(4)-P and NH(4)(+) during precipitation in a batch reactor, resulted in a good estimation of the effluent PO(4)-P concentration of the pilot plant, operating under continuous mode. X-ray diffraction (XRD) analyses confirmed the presence of struvite in the small single crystals observed during experiments. The operational cost for the ureolytic MAP crystallization treating high phosphate concentrations (e.g. 100 mg · L(-1) PO(4)-P) was calculated as 3.9 € kg(-1) P(removed). This work shows that the ureolytic MAP crystallization, in combination with an autotrophic nitrogen removal process, is competitive with the NuReSys(?) technology in terms of operational cost and removal efficiency but further research is necessary to obtain larger crystals.     

Predicting struvite formation for phosphorus recovery from human urine using an equilibrium model.

Interest in phosphorus recovery from urine diverted from faeces has been growing recently. Phosphorus in urine can be precipitated out as struvite (MgNH4PO4 x 6H2O) with addition of magnesium salt under alkaline conditions. Struvite formation, however, should be more well understood for its practical application. We predicted the struvite formation with a development of a new equilibrium model. The model considered the formation of eight different kinds of precipitates, including struvite, with effects of ionic strength and temperature. In addition, experiments on struvite formation in urine were conducted for the model validation. The model prediction of struvite formation had good agreement with the experimental results. The optimum pH to form struvite was predicted to be 9.4-9.7. In order to precipitate 99% of phosphate in urine with 1.5 fold Mg concentration to PO4-P, the pH value was necessary to be more than 8.1 based on the model prediction.     

Raw water quality weight factors: Vaal basin, South Africa

Weight factors (WFs) were developed for surface raw water pollution indicator variables in Vaal River's Upper and Middle Vaal sub-basins, in South Africa. The overall objective was to formulate a quantifiable ranking system to indicate importance of pollutant variables given their established effects on human and environmental health. Multi-criteria decision analysis (MCDA) was applied to qualitative data that were obtained from South Africa's target water quality ranges as well as from literature which represented expert opinion. The human and environmental health effect choice sets were ranked from 1 to 5 on nine pollutant variable criteria: NH3/NH4+, Cl-, conductivity (EC), dissolved oxygen (DO), pH, F-, NO3-/NO2-, PO4(3-) and SO4(2-). The weighted-sum method (WSM) then assigned highest and lowest normalised weights (NWs) to F- and Cl-, respectively, for human health effects (?hh) alternative. Highest and lowest NWs were assigned to NH3/NH4+ and EC, respectively, for environmental health effects (?eh) alternative. After aggregating the ?hh and ?eh WFs, resultant values ranked the variables from highest to lowest as follows: F->NO3-/NO2->/NH3/NH4+>DO>pH>SO4(2-)>PO4(3-)>EC>Cl-. The results represented the importance of variables given their established effects on human and environmental health. It was concluded that WFs provided a quantifiable barometer which could signal harmful exposure to elucidate negative effects of using polluted surface raw water in the study area. The values could be incorporated into water quality models like water quality indices. The approach could be used to develop WFs for other sites, taking into account issues like the site's pollution variables of concern as well as using a ranking key constructed from established literature.     

Zeta potential measurement on the surface of blue-green algae particles for micro-bubble process.

Any kind of blue-green alga produces metabolites of musty substances and toxins. Therefore, it is necessary to remove the blue-green algae, and processing also including nutrient removal is desired for the water quality improvement of eutrophic lakes. The purpose of this study has been to investigate the possibility of a flotation system using a hybrid technique (chemical compounds and electrostatic bridge) applied to raw water containing phytoplankton with high pH of water, and to examine the zeta potential value of phytoplankton surface and the removal efficiency for phytoplankton, ammonia, nitrogen, and phosphoric acid.The results were as follows: firstly, zeta potential of M. aeruginosa particles was observed to achieve charge neutralization on their surface by adhesion of magnesium hydroxide precipitation with increasing pH. Secondly, maximum removal efficiency concerning chlorophyll-a was observed as 84%, and this efficiency was obtained in the condition of pH > 10, and magnesium hydroxide precipitation was observed. Thirdly, in the pH condition that the maximum removal efficiency of chlorophyll-a was obtained, the removal efficiency and the amount of decrease of NH(4)-N and PO(4)-P before and after the change of pH values were observed as 6.7% (0.04 mg-P/L) and 63.6% (0.07 mg-N/L), respectively.     

Phosphorus recovery from wastewater through struvite formation in fluidized bed reactors: a sustainable approach.

Recovery of phosphate as struvite (MgNH4PO4.6H2O), before it forms and accumulates on wastewater treatment equipment, solves wastewater treatment problems and also provides environmentally sustainable, renewable nutrient source for the agriculture sector. A pilot-scale fluidized bed reactor was used to recover phosphate through crystallization of struvite, from anaerobic digester centrate at the Lulu Island Wastewater Treatment Plant, Richmond, British Columbia, Canada. The desired degree of phosphate removal was achieved by maintaining operating pH (8.0-8.2), and recycle ratio 5-9, to control the supersaturation conditions inside the reactor. The performance of the system was found to be optimal when in-reactor supersaturation ratio was 2-6. Among several other operating parameters, apparent upflow velocity and magnesium to phosphate molar ratio were also found important to maintain system performance, both in terms of efficiency of phosphate removal and recovery as struvite pellets. A narrow window of upflow velocity (400-410 cm/min) was found to be effective in removing 75-85% phosphate. TOC level inside the rector was found to affect the performance to some extent. The precipitation potential of struvite could be successfully predicted using a thermodynamic solubility product value of 10(-13.36) and its temperature dependence in PHREEQC.     

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.     

An innovative technology based on aerobic granular biomass for treating municipal and/or industrial wastewater with low environmental impact.

The paper reports the results of an investigation carried out at lab scale to assess the effectiveness of an innovative technology (SUPERBIO) for treating municipal and/or industrial wastewater. When this technology was applied for treating municipal wastewater, the results showed that even at maximum organic load (i.e. 7 kg COD m(-3) d(-1)), the COD in the treated effluent was lower than 50 mg L(-1). In addition, both ammonia and TKN removal efficiencies resulted in higher than 87% up to an organic load of 5.7 kg COD m(-3) d(-1) corresponding to a nitrogen load of 0.8 kg TKN m(-3) d(-1). Very satisfactory process performances also resulted during tannery wastewater treatment, when a chemical oxidation step (i.e. ozonation) was inserted in the treatment cycle of SUPERBIO. In such an instance, at organic and nitrogen loadings of 3 kgCOD m(-3) d(-1) and 0.20 kg N m(-3) d(-1), COD, NH4+ -N and TSS average removals were 96, 99 and 98%, respectively. Finally, during the whole experimentation, SUPERBIO was always characterised by a very low sludge production. Such a result was ascribed mainly to the characteristics of biomass that grew in the form of very dense granules (i.e. 130 gVSS L(Biomass)(-1) allowing a biomass concentration as high as 50-60 gTSS l(bed)(-1) to be achieved.     

Investigating the spatial-temporal variation of nitrogen cycling in an urban river in the North China Plain

Urban rivers are essential in retaining nutrients, but little is known about nitrogen cycling in these rivers in semiarid areas. We measured chemical and isotopic compositions of ammonium (NH4(+)-N) and nitrate (NO3(-)-N) to investigate spatial-temporal variation of nitrogen cycling in the Fuhe River in the North China Plain. Nitrogen pollution in the river was mainly induced by extra NH4(+)-N inputs which come from the discharges of urban sewage and effluents of wastewater treatment plants in upstream. NH4(+)-N obtained from decomposing organic matter of sediments can diffuse into the overlying water. Intense nitrification then occurs at the terrestrial-aquatic interface. Due to less vegetation in spring and autumn, loss of NH4(+)-N is mainly caused by nitrification. In contrast, significant NH4(+)-N is absorbed by plants in summer. NO3(-)-N generated from nitrification can be denitrified during the study period. The highest NO3(-)-N loss (about 86.3%) was observed in summer. The contribution of NO3(-)-N loss due to denitrification is 44.6%. The remaining 55.4% is due to plant uptake. The results suggested that nitrogen cycling in the river is related to temperature and dry-wet cycles. And vegetation restoration along the river could benefit the incremental improvements to the aquatic ecosystem.     

Forecasting influent flow rate and composition with occasional data for supervisory management system by time series model.

The information on the incoming load to wastewater treatment plants is not often available to apply modelling for evaluating the effect of control actions on a full-scale plant. In this paper, a time series model was developed to forecast flow rate, COD, NH4(+)-N and PO4(3-)-P in influent by using 250 days data of field plant operation data. The data for 150 days and 100 days were used for model development and model validation, respectively. The missing data were interpolated by the spline method and the time series model. Three different methods were proposed for model development: one model and one-step to seven-step ahead forecasting (Method 1); seven models and one-step-ahead forecasting (Method 2); and one model and one-step-ahead forecasting (Method 3). Method 3 featured only one-step-ahead forecasting that could avoid the accumulated error and give simple estimation of coefficients. Therefore, Method 3 was the reliable approach to developing the time series model for the purpose of this research.