Specific oxygen, ammonia, and nitrate uptake rates of a biological nutrient removal process treating elevated salinity wastewater

Anaerobic/anoxic/aerobic systems inoculated without and with NaCl acclimated cultures, i.e., Models A and B, respectively, were fed with a synthetic wastewater at various salinity levels. After achieving a steady state, the systems were shocked with 70 g/l NaCl for four consecutive days before returning to pre-shock conditions. At the steady-state, the specific oxygen uptake rates (SOURs) increased with an increase of sodium chloride concentration (from 5.40 to 9.72 mg O₂/g mixed liquor suspended solids (MLSS)-h at 0–30 g/l NaCl for Model A and from 6.84 to 17.64 mg O₂/g MLSS-h at 5–30 g/l NaCl for Model B). In contrast, the specific ammonia uptake rate (SAUR) and specific nitrate uptake rate (SNUR) decreased with increasing chloride concentration (from 4.76 to 2.14 mg NH₃–N/g MLSS-h and 2.50 to 1.22 NO3–N/g MLSS-h, for Model A, and from 3.84 to 2.71 mg NH₃–N/g MLSS-hr and 2.54 to 1.82 mg NO₃–N/g MLSS-hr, for Model B). During the shocked period, the SOUR in most scenarios increased whereas the SAUR and SNUR tended to decrease. The impact of the chloride shock on nitrifiers was more obvious than on denitrifiers; however, after a certain recovery period, the activities of both nitrifiers and denitrifiers in terms of SAUR and SNUR were approximately the same as those prior to shock.     

Ammonia emissions during the initial phase of microbial degradation of solid and liquid cattle manure

The maximum specific ammonia emissions from liquid manure (LM) and solid manure containing 2.5 kg straw/livestock unit (LU)/day (SM 2.5) or 15 kg straw/LU/day (SM 15) increased in the sequence LM < SM 2.5 < SM 15 (662.6 < 3163.7 < 6299.8 μg NH₃–N/h/kg). These emission levels were attained soon after the maximum temperatures (22.9°C < 34.3°C < 69.5°C) induced by microbial self-heating had been reached. After that, NH₄⁺ was microbially re-bound in amounts that increased with a higher C content and a widening C:N ratio, i.e. also in the sequence LM < SM 2.5 < SM 15. Over a period of 15 to 16 days, 6.0% (LM), 10.8% (SM 2.5) and 5.9% (SM 15) of the N_total was emitted. When the accumulated ammonia emissions were extrapolated beyond this period of investigation, it was concluded that, over longer storage periods, solid manure offers better biological conditions for low ammonia emissions than liquid manure.     

Nutrient removal by thermophilic Fischerella (Mastigocladus laminosus) in a simulated algaculture process

A novel nutrient removal/waste heat utilization process was simulated using semicontinuous cultures of the thermophilic cyanobacterium Fischerella. Dissolved inorganic carbon (DIC)-enriched cultures, maintained with 10 mg l⁻¹ daily productivity, diurnally varying temperature (from 55°C to 26–28°C), a 12:12 light cycle (200 μE sec⁻¹ m⁻²) and 50% biomass recycling into heated effluent at the beginning of each light period, removed > 95% of NO₃⁻ + NO₂⁻−N, 71% of NH₃-N, 82% of PO₄³⁻ −P, and 70% of total P from effluent water samples containing approximately 400 μg l⁻¹ combined N and 60 μg l⁻¹ P. Nutrient removal was not severely impaired by an altered temperature gradient, doubled light intensity, or DIC limitation. Recycling 75% of the biomass at the end of each light period resulted in unimpaired NO₃⁻ + NO₂⁻ removal, 38–45% P removal and no net NH₃ removal. Diurnally varying P removal, averaging 50–60%, and nearly constant > 80% N removal, are therefore projected for a full-scale process with continuous biomass recycling.     

氮素形态对樱桃番茄果实发育中氮代谢的影响

以樱桃番茄为材料,采用基质 营养液共培养的方法,研究了全硝态氮(NO₃^-）、铵态氮和硝态氮配施（75%NO₃^-∶25%NH₄⁺）及全铵态氮（NH₄⁺）营养对樱桃番茄果实氮代谢及硝酸还原酶（NR）和谷氨酰胺合成酶（GS）基因表达的影响.结果表明： 铵态氮和硝态氮配施处理下樱桃番茄的单果质量比全硝态氮处理略有增加,且果实中NH₄⁺、总氨基酸、氮含量和氮素累积量均显著高于全硝态氮处理;全硝态氮及铵态氮和硝态氮配施处理下果实NR活性及其基因表达没有明显差异,但都显著高于全铵态氮处理;铵态氮和硝态氮配施处理下果实GS活性都高于全硝态氮处理.不同形态氮素及配施处理下,同工酶GS1（胞质型GS）和GS2（叶绿体型GS）的表达与GS的活性不一致,说明氮素对GS活性的影响主要发生在转录后水平.     

Phytoavailability assessment of heavy metals in soils by single extractions and accumulation by Phaseolus vulgaris

In Western Europe, policy makers are currently moving towards a more integrated risk-based approach of soil contamination assessment. As part of this approach, selective single extraction procedures have been proposed to add complementary insights regarding heavy metal behaviour and phytoavailability in soils and sediments. However, there is currently a wide range of such procedures available in literature, hampering standardisation and harmonisation of phytoavailability research of heavy metals. The current study examines shoot accumulation of Cd, Cu, Ni, Pb and Zn by the test plant Phaseolus vulgaris in 21 soils, differing in soil composition and level of contamination. On these soils, 12 different commonly used extraction procedures have been compared: soil solution extraction by Rhizon soil moisture samplers, 0.01 M CaCl₂, 0.1 M NaNO₃, 1 M NH₄NO₃, 1 M NH₄NOAc, 1 M MgCl₂, 0.11 M HOAc, 0.5 M HNO₃, 0.1 M HCl, DTPA–TEA–CaCl₂, EDTA-NH₄OAc and aqua regia. The plant species used in this study has previously been proposed as a test plant in a bioassay for assessing heavy metal induced oxidative stress in contaminated soils [Van Assche, F., Clijsters, H., 1990. A biological test system for the evaluation of the phytotoxicity of metal-contaminated soils. Environ. Pollut., 66, 157–172]. Cadmium shoot accumulation correlated best with soil solution concentrations, unbuffered nitrate solutions and the dilute CaCl₂ extraction procedure. The same was observed for Zn, yet for this element NH₄OAc and MgCl₂ also provided significant interactions. The best prediction for Ni was observed in the cluster containing CaCl₂ and NH₄NO₃. For Cd, Zn and Ni, the pseudo-total content and the aggressive chelate based and/or acidic extractants did not correlate well with shoot accumulation. Cu and Pb uptake on the other hand was found to correlate significantly (p = 0.01) with total content as well as with all aggressive extraction procedures over the range of soils used in this experiment. In general, the 0.01 M CaCl₂ extraction procedure proved to be the most versatile as it provided a good indication of phytoavailability for all five metals under evaluation.     

Biodegradation of waste-lubricating petroleum oil in a tropical alfisol as mediated by animal droppings

This study evaluated the applicability of some organic wastes from animal droppings as bioremediation alternative for soils spiked with waste-lubricating oil (spent oil). The total hydrocarbon contents (THC) with time of sampling were markedly reduced with addition of cow dung (CD), poultry manure (PM) and pig wastes (PW). The general trend in the first year indicated that PW stimulated the highest net percentage loss in THC for soils polluted with 5000 mg kg⁻¹ (0.5%SP) and 50,000 mg kg⁻¹ (5%SP) oil levels. Poultry manure induced the highest reduction in soils polluted with medium, i.e. 2.5%SP (25,000 mg kg⁻¹) oil concentration. The overall net loss mediated by each organic waste in the 2nd year showed that PM addition was better irrespective of total oil loading. For example, at 3 months PM led to 16.1% and 14.6% net reduction in THC for soils treated with 50,000 mg kg⁻¹ (5%) and 100,000 mg kg⁻¹ (10%) total oil loading, respectively; whereas at same period, the performance of the organic wastes were relatively similar in soils with 10,000 mg kg⁻¹ oil loading. At 6 and 12 months, PM reduced the oil levels better than CD and PW. Further evaluation by first-order kinetic model which utilized combine data for the entire periods for each year indicated that PW was better at low oil pollution level, while PM performed better at high oil pollution levels. Overall, the differential performance of these organic amendments followed PM > PW > CD.     

高效氮肥对新疆膜下滴灌棉田土壤氧化亚氮排放的影响

高效氮肥对新疆灰漠土农田氧化亚氮(N₂O)排放的影响目前尚不明确.本研究选取树脂包膜尿素(ESN)和尿素配施脲酶抑制剂和硝化抑制剂(U+I)两种高效氮肥处理,以传统尿素(U)处理为对照,研究高效氮肥对新疆膜下滴灌棉田N₂O排放的影响.ESN在播种时一次性施入,而其他处理的氮肥在生育期内随灌溉分次施入.在生育期内,采用静态箱-气相色谱法每周采集和分析2次气体样品.结果表明: 与其他处理相比,ESN处理显著增加了生育期间土壤N₂O的排放量,增幅47%～73%;在施肥后的4个月内,ESN处理下的土壤铵态氮(NH₄⁺-N)和硝态氮(NO₃^--N)含量始终处于较高水平,随后则逐渐减小并与其他处理的含量相近.ESN在播种时全部施入可能是导致土壤高NH₄⁺-N和NO₃^--N含量以及高N₂O排放量的原因.与U处理相比,U+I处理减少了9.9%的N₂O排放量,但两者间差异不显著;U+I处理NO₃^--N含量始终低于ESN和U处理.新疆灰漠土膜下滴灌棉田生育期土壤的N₂O排放为300～500 g N₂O-N·hm^-2,整体低于其他农田生态系统.与播种前全部施入相比,氮肥随滴灌多次施入更利于降低N₂O排放.本试验条件下,高效氮肥对干旱区膜下滴灌棉田土壤N₂O的减排效应有限.     

Nitrogen mineralisation and plant nitrogen acquisition in a nitrogen-limited calcareous grassland

A field study measured the rate of soil mineral N supply and its effects on plant biomass and N accumulation in a 13-year-old, naturally regenerating, calcareous grassland. Gross rates of N mineralisation (2 μg g⁻¹ day⁻¹, i.e. 0.69 kg ha⁻¹ day⁻¹), assessed using ¹⁵N pool dilution, were at the lower end of the range previously reported for grasslands. Weekly additions of liquid N fertiliser ([NH₄]₂SO₄, NH₄NO₃ or KNO₃) and, to a lesser extent the addition of water, increased plant growth substantially, demonstrating that the primary constraint to plant growth was low N availability. In plants that had received NO₃⁻, the activity of the inducible enzyme nitrate reductase in shoots initially increased in proportion to the amount of NO₃⁻ supplied. However, as above-ground herbage accumulated, nitrate reductase activity declined to similar low levels in all treatments, despite the continuance of the constant NO₃⁻ additions. The decline in NR specific activity reflected declining tissue NO₃⁻ concentrations, although total plant NRA may have remained constant during the period of study. The study has shown that plant growth is limited by low N mineralisation rates and indeed the soil is a sink for much added N. Low water availability provides an additional constraint on N mineralisation in this calcareous grassland soil. Any disturbances in the N cycle which increase the availability of mineral N will result in a substantial increase in plant growth within this ecosystem.     

Comparison of bio-augmentation and composting for remediation of oily sludge: A field-scale study in China

Two bioremediation technologies were performed in order to explore a better treatment process for an oily sludge restoration in China during 2004. The bioremediation by augmentation of biopreparation was compared with a conventional composting. The oily sludge and oil-polluted soil were received from an oil production plant. The total hydrocarbon content (THC) varied from 327.7 to 371.2 g kg⁻¹ of dry sludge and the THC in contaminated soil was 151.0 g kg⁻¹. Before application of preparation, straw, sawdust, top sand and pure soil were added in different proportions to the sludge and soil and mixed thoroughly. Such sludge and soil composites were used for negative controls and for activation of indigenous oil degrading microorganisms with addition of fertilizer (positive controls). For composting, crude manure and straw were added to the oily sludge and the THC was 101.4 g kg⁻¹. The biopreparation was applied every 2 weeks and experiment lasted 56 days under the ambient temperature. The sludge was mixed and watered every 3 days. After three times of biopreparation application, the THC decreased by 46–53% in the oily sludge and soil, while in the positive controls (activation of indigenous microorganisms) the THC decreased by 13–23%, and there was no oil degradation in negative controls After composting, the THC decreased by 31% in the oily sludge. The planting of Tall Fescue (Festuca arundinace) revealed a decrease of sludge toxicity after application of both bioremediation technologies and additionally decreased the THC by 5–7%.     

The stereochemistry of Co(III)-amine complexes. The use of nOe and COSY H NMR spectroscopy to determine structure in solution

It is shown how 1D nOe and 2D COSY ¹H NMR spectroscopy can be used to assign the stereochemistry of Co(III) amine complexes. By using d₆-DMSO as solvent together with a small quantity of DCl all non-equivalent N---H hydrogens can be distinguished at 300 MHz. Through-space (nOe), and through-bond (COSY), associations with other N---H and C---H hydrogens can then be determined. This leads to a complete assignment of structure in solution. The technique is applied to the complexes syn(N), anti(N)-[Co(cyclen) (NH₃)₂] (ClO₄)₃, syn(N), anti(Cl)-[Co(cyclen) (NH₃)Cl] (ClO₄)₂, anti(N), syn(Cl)-[Co(cyclen) (NH₃)Cl](ClO₄)₂, syn(N), anti(O)-[Co(Mecyclen)-(GlyO)](ClO₄)₂ and Δ-cis-[Co(δ-en)₂(NO₂)₂](NO₂).     

较长时间内15N标记的氨态氮和硝态氮在小嵩草草甸中的运移规律

运用15N稳定性同位素技术,对15N标记的硝酸盐和铵盐在输入小嵩草(Kobresia pygaea C.B.Clarke)草甸11～13个月后的运移规律进行了研究.在经历11～13个月后,进入无机氮库中的15N很少,一般不超过所输入氮素的l%,而较多的1 5N为土壤有机质、土壤微生物和植物所固持.NO3--15N和NH4 -1 5N在小嵩草草甸中的运移规律差异很大.在11、12和13个月后,NO3--15N的总恢复率分别为92.83%、92.64%和79.96%;而NH4 -15N的则分别为49.6%、63.33%和66.22%.两者的差异在土壤有机质、土壤微生物和植物等库之间的分配中更加明显.输入NO3--15N时在11、12个月后植物所固持的15N最多,而土壤微生物和土壤有机质所固持的15N比较接近,而在13个月后,土壤有机质和植物所固持的15N接近,而土壤微生物所固持的15N下降许多;当输入NH4 -15N,土壤有机质所固持的1 5N比植物和土壤微生物所固持的都多,而且植物所固持的15N比较稳定,而土壤微生物所固持的15N则有较大变化.这表明在较长的时间内嵩草草甸对NO3-和NH4 的固持能力是不一样的.     

Responses of plant community biomass to nitrogen and phosphorus additions in natural and restored grasslands around Qinghai Lake Basin

Aims Plant biomass reflects the primary productivity of community vegetation, and is the main resource of carbon input in the terrestrial ecosystem. It is usually limited by nitrogen (N) and phosphorus (P) availability in the soil. Alpine grassland around Qinghai Lake Basin has experienced extensive land-use changes due to the cultivation of native grassland and vegetation recovery on cropped land. In this experiment, two grassland types were chosen, natural alpine grassland (NG) and its adjacent restored grassland (RG), to determine the responses of plant community biomass to N and P additions with different land-use. Methods NH₄NO₃ and Ca(H₂PO₄)₂·H₂O were added in a completely randomized block design, with medium levels of 10 g N·m^-2 and 5 g P·m^-2. Soil NO₃^--N and available P contents, and the plant community biomass were measured in the two grasslands. Two-way ANOVA was used to determine the effects of nutrient additions on all measured indicators, and regression analysis was used to analyze the correlations between plant biomass and soil NO₃^--N and available P contents.Important findings Results showed: (1) N and P additions both increased grass biomass in the NG, and significantly elevated the total aboveground biomass, with the promoting effect of N addition higher than that of P addition; N addition significantly increased both grass and forb biomass in the RG, and markedly promoted the total aboveground biomass, while P addition had no effects on the functional groups and total aboveground biomass (p > 0.05). (2) N and P additions both had no effects on the belowground and total biomass in the NG, whereas N addition significantly increased the total biomass by 34% in the RG, which suggested that the effect of N limitation on the vegetation primary productivity was stronger in the RG at present stage. (3) The aboveground biomass in the NG increased with soil NO₃^--N content (p < 0.05), and the above- and below-ground as well as the total biomass were all positively correlated with soil NO₃^--N content in the RG (p < 0.01). These results indicated that the plant growth in alpine grassland around Qinghai Lake Basin was prone to N limitation, and the effect of P limitation changed with land-use. Soil available N might be the key limiting factor for vegetation restoration and reconstruction in the RG. The “Grain for Green” project (the land-use policy) and atmospheric N deposition are benefiting both plant growth and C accumulation in the alpine grassland ecosystem around Qinghai Lake Basin.     

环青海湖地区天然草地和退耕恢复草地植物群落生物量对氮、磷添加的响应

植物群落生物量反映了植被的初级生产能力, 是陆地生态系统碳(C)输入的最主要来源, 往往受到自然界中氮(N)、磷(P)元素供应的限制。该试验以青藏高原环青海湖地区的高寒草原为研究对象, 探讨了天然草地和退耕恢复草地植被群落生物量对N (10 g·m^-2)、P (5 g·m^-2)养分添加的响应。N、P添加显著增加了天然草地禾草的生物量, 进而促使地上总生物量显著提高。退耕恢复草地禾草和杂类草的生物量对N添加均有一致的正响应, 从而促使地上总生物量显著增加174%, 群落地上和地下总生物量显著增加34%; 而P添加对恢复草地生物量各项参数均无显著影响。回归分析显示: 天然草地植物群落地上生物量随土壤中NO₃^--N含量的增加而增加(p < 0.05), 退耕恢复草地植被地上、地下和总生物量均与土壤NO₃^--N含量显著正相关(p < 0.01), 说明环湖地区高寒草原植物生长主要受N供应的限制, P的限制作用随土地利用方式的转变和群落演替阶段的不同而变化; 相比天然草地, 恢复草地在现阶段植被初级生产力受N的限制作用更强烈, 土壤中可利用N含量是限制其植被自然恢复和重建的关键因子。     

氮肥形态及配比对花椰菜产量、品质和养分吸收的影响

采用大田试验研究了氮肥不同形态及配比对春茬花椰菜产量形成、品质和植株氮、磷、钾吸收的影响.结果表明:硝态氮肥易增加花球中硝酸盐的积累量、提高可溶性糖含量,当NO₃^--N∶NH₄⁺-N处于3∶7～5∶5范围内时可以减少花球中硝酸盐积累量,处于5∶5～7∶3范围内时可获得较高的可溶性糖含量.铵态氮肥(包括酰胺态氮肥)有利于花球中Vc含量的提高.施氮肥可以提高植株中氮、磷、钾的积累量,其中莲座期各处理植株氮、磷、钾含量均为最高.在整个生长期铵态氮有利于促进氮含量的提高,硝态氮有利于钾含量的提高,但在不同时期磷含量受氮源的影响变化不一致.与单一氮肥形态相比,当NO₃^--N∶NH₄⁺-N处于3∶7～5∶5范围内时易获得高产.因此硝态氮肥与铵态氮肥以适当的比例配合施用可以提高花椰菜的品质、生物产量和经济效益.     

Nitrogen preference across generations under changing ammonium nitrate ratios

Aims Nitrogen (N) in natural environments is typically supplied by a mixture of ammonia (NH₄⁺) and nitrate (NO₃^-). However, factors that underlie either NH₄⁺or NO₃^-preference, and how such preference will change across generations remain unclear. We conducted a series of experiments to answer whether: (i) NH₄⁺:NO₃^-ratio is the driving factor for plant N preference, and (ii) this preference is consistent across generations.     

低氮胁迫诱导木薯幼苗花青素积累及其基因表达

为明确氮素浓度和形态与木薯花青素产生和积累的关系,基于氮素胁迫能够在拟南芥等植物中促进花青素产生的研究结果,以木薯品种Arg7为研究对象,研究木薯无菌幼苗在添加了(1)40 mmol/L NO₃^-+ 20 mmol/L NH₄⁺,(2)40 mmol/L NO₃^-,(3)20 mmol/L NH₄⁺,(4)0.4 mmol/L NO₃^-+ 0.2 mmol/L NH₄⁺,(5)0.4 mmol/L NO₃^-,(6)0.2 mmol/L NH₄⁺,(7)1 mmol/L(N),(8)5 mmol/L(N),(9)9 mmol/L(N),(10)13 mmol/L(N)10种氮素浓度和形态的MS培养基中生长40 d的农艺性状,以及对花青素合成相...     

夜间增温对亚高山针叶林主要树种无机氮吸收的影响

吸收营养物质是植物根系的主要生理功能。氮素吸收是植物体内氮代谢的第一步, 也是最关键的一步。为了全面地认识亚高山针叶林在全球气候变化背景下对两种主要无机氮(NH₄⁺和NO₃^-)吸收特点的变化, 该研究以川西亚高山针叶林优势树种——云杉(Picea asperata)和岷江冷杉(Abies fargesii var. faxoniana)为材料, 通过红外辐射加热器模拟增温, 利用非损伤微测技术(non-invasive micromeasurement technology)研究了这两个树种吸收NH₄⁺和NO₃^-特点的变化, 同时还探究了NH₄⁺和NO₃^- 之间的相互作用对植物吸收这两种离子的影响。研究结果显示: 在云杉根系中, NH₄⁺和NO₃^-的最大吸收速率分别发生在距离根尖最顶端17-18 mm区域和17 mm处, 而岷江冷杉对这两种离子的最大吸收速率分别发生在距离根尖顶端11 mm和11.5 mm处。增温对云杉和岷江冷杉根系吸收NH₄⁺和NO₃^-有促进作用。在增温条件下, NO₃^-能够促进云杉根系对NH₄⁺的吸收, 而NH₄⁺则抑制了其对NO₃^-的吸收。无论是否增温, 岷江冷杉对NH₄⁺的吸收都不受NO₃^-的影响, 而在增温条件下, NH₄⁺会抑制岷江冷杉对NO₃^-的吸收。     

Removal of ammoniacal-nitrogen from an artificial landfill leachate in downflow reed beds

The fate of ammoniacal-nitrogen (NH₄-N) was studied in a lab-scale downflow reed bed system treating an artificial landfill leachate. Individual reed beds were saturated by the leachate, then drained and rinsed by tap water. NH₄-N was removed by a two-stage process, adsorption onto the reed bed media followed by nitrification into nitrite-nitrogen (NO₂-N) and nitrate-nitrogen (NO₃-N). Decrease of the NH₄-N level of the leachate was observed when the reed beds were saturated. By rinsing the beds, part of the NH₄-N adsorbed inside the bed matrices was released into the rinse water. The presence of NO₂- and NO₃-N in the rinse water demonstrated that nitrification took place while NH₄-N was retained inside the bed matrices. For artificial leachates with NH₄-N levels of 150±5 mg/l, an average removal rate of 44% in a 3 h treatment was achieved. Mass balance analysis indicated that adsorption, transformations into NO₂- and NO₃-N accounted for 64, 4 and 24% of the NH₄-N removal, respectively. This study also demonstrated that in general a greater rate of effluent recirculation around downflow reed beds gives higher NH₄-N removal.     

苦草根系对硝氮和氨氮的吸收

硝氮(NO₃^--N)和氨氮(NH₄⁺-N)是湖泊沉积物间隙水生物可利用氮源的主要形态。论文通过稳定性同位素¹⁵N示踪技术,通过模拟实验分别研究了苦草根系对NH₄⁺-N和NO₃^--N的吸收及其与氮浓度的关系。结果显示,苦草(Vallisnerianatan)根系对NH₄⁺-N的吸收显著高于NO₃^--N;根系吸收氮后向叶转移,而且NO₃^--N为氮源时其转移速率较高;NH₄⁺-N浓度的变化对苦草吸收NO₃^--N有影响,当NH₄⁺-N浓度小于0.072mmol/L时,根系对NO₃^--N的吸收随NH₄⁺-N浓度的增加而增加,随后降低并趋于平稳;同时,NO₃^--N浓度对苦草吸收NH₄⁺-N也有类似的影响。     

Ammonia removal from anaerobically digested dairy manure by struvite precipitation

Ammonia is one of the most important contaminants impairing the quality of water resources. When this is considered along with the fact that the global demand for nitrogenous fertilizers is in constant rise, the need for recovery as well as removal of nitrogen is well justified. Crystallization of N and P in the form of struvite (MgNH₄PO₄·6H₂O), which is a slow releasing and valuable fertilizer, is one possible technique for this purpose. This study investigated the removal of NH₄⁺ through struvite precipitation from the effluents of one- (R1) and two-phase (R2) anaerobic reactors digesting dairy manure. To force the formation of struvite in the anaerobic reactor effluents, Mg²⁺ ion was added by using both Mg(OH)₂ and MgCl₂·6H₂O. To prevent the effect of different total phosphorus (TP) concentration in the effluents of R1 and R2, as well as to not limit the formation of struvite, an excess amount of PO₄³⁻ (0.14 M) was added in the form of Na₂HPO₄. Different stoichiometric Mg²⁺:NH₄⁺:PO₄³⁻ ratios were tested to determine the required Mg²⁺ concentrations for maximum NH₄⁺ removal by keeping NH₄⁺:PO₄³⁻ ratio constant for the effluents of reactors R1 and R2. The results revealed that very high NH₄⁺ removal efficiencies (above 95%) were possible by adding Mg²⁺ ions higher than 0.06 M concentration in the effluents from reactors R1 and R2. It was also observed that the initial pH adjustment to 8.50 using NaOH did not result in any significant increase in the removal of NH₄⁺ and the removal of NH₄⁺ in the reactors treated with MgCl₂·6H₂O was higher than those treated with Mg(OH)₂ for the same Mg²⁺ concentration.