An economic evaluation of phosphorus recovery as struvite from digester supernatant

Phosphorus can be recovered from wastewater through crystallisation of struvite, MgNH(4)PO(4).6H(2)O. Approximately 1 kg of struvite can be crystallised from 100 m(3) of wastewater. Crystallisation is profitable compared to chemical and biological removal of phosphorus due to savings from the reduction in (i) chemicals used for precipitation and sludge disposal; and (ii) downtime for cleaning unwanted struvite formed during chemical and biological removal. The struvite produced annually from a wastewater treatment plant that processed 100 m3/d, would be sufficient to apply on 2.6 ha of arable land, as fertilizer. If struvite were to be recovered from wastewater treatment plants worldwide, 0.63 million tons of phosphorus (as P(2)O(5)) could be harvested annually, reducing phosphate rock mining by 1.6%. Therefore, this technology could provide opportunities to recover phosphorus sustainably from waste streams and preserve phosphorus reserves.     

A pilot-scale study of struvite precipitation in a stirred tank reactor: conditions influencing the process

Currently, the two most developed techniques for recovering phosphorus from wastewater consist of the formation of calcium phosphates and struvite (MgNH(4)PO(4).6H(2)O). In this work the influence of the operational conditions on the struvite precipitation process (pH in the reactor, hydraulic retention time, and magnesium:phosphorus, nitrogen:phosphorus, and calcium:magnesium molar ratios) have been studied. Twenty-three experiments with artificial wastewater were performed in a stirred reactor. In order to obtain the pH value maintenance during the crystallization process, a fuzzy logic control has been developed. High phosphorus removal efficiencies were reliably achieved precipitating the struvite as easily dried crystals or as pellets made up of agglomerated crystals.     

Application of struvite precipitation as a pretreatment in treating swine wastewater

In this study, the effect of the pretreatment of NH₄-N by struvite precipitation on biological nitrogen removal was investigated in treating swine wastewater. Evaluation was mainly focused on nitrification which occurred in the activated sludge system after struvite precipitation. Laboratory experiments were performed at four different hydraulic retention times (HRT), i.e., 48, 32, 24 and 16 h. Results of the long-term operation of systems showed that the struvite precipitation used as the pretreatment of raw swine wastewater enhanced the nitrification performance in activated sludge system by reducing the applied loading rates of NH₄-N and TCOD in all operating conditions. The reduction of the applied NH₄-N loading rate kept the levels of free ammonia (FA) concentration in biological reactors low and it prevented nitrite accumulation. In addition, the struvite precipitation elicited the biological denitrification reaction and PO₄-P removal by increasing the ratios of carbon-to-nitrogen and carbon-to-phosphorus of wastewater after struvite precipitation. The struvite precipitation also enhanced the biological TCOD removal performance by reducing the toxic effect of FA. Triplicate INT-dehydrogenase tests clearly showed that FA inhibited the degradation of organic matter in activated sludge system. Finally, the struvite precipitation contributed to high TCOD, T-N and PO₄-P removals of 83, 90, and 97% by facilitating biological reaction at a short HRT of 16 h.     

Effect of mixing on spontaneous struvite precipitation from semiconductor wastewater

The objective of this study was to investigate on the effect of mixing intensity (G) and mixing duration (t(d)) on struvite precipitation in the chemical mechanical polishing (CMP) wastewater generated from the semiconductor manufacturing process. Batch-scale experiments revealed that struvite crystallization was affected by both G and t(d). The mixing effect was to enhance the mass transfer of solute to the crystals in the process, resulting in the improvement of struvite crystallization and growth. By forming struvite, removal efficiencies of N and P increased logarithmic with the multiple values of G and t(d), i.e., Gt(d). Insufficient mixing energy with the Gt(d) value less than 10(5) caused an increase in the formation potential of unexpected precipitate unlike to pure struvite, causing a decrease in removal efficiencies of N and P in the process. At the Gt(d) value over 10(6), struvite precipitation was not restricted by fluoride, of which high level inherently contained in the CMP wastewater. The study results can be taken into consideration in the design and operation of the struvite precipitation process for both nutrient (N and P) removal and recovery.     

Removal of nutrients from piggery wastewater using struvite precipitation and pyrogenation technology

In this paper, removal of nutrients from piggery wastewater by struvite crystallization was conducted using a combined technology of low-cost magnesium source in struvite precipitation and recycling of the struvite pyrolysate in the process. In the present research, it was found that high concentrations of K⁺ and Ca²⁺ present in the solution significantly affected the removal of nutrients. When the struvite crystallization formed at the condition of dosing the magnesite pyrolysate at a Mg:N:P molar ratio of 2.5:1:1, and having a reaction time of 6 h, a majority of nutrients in piggery wastewater can be removed. Surface characterization analysis demonstrated that the main components of the pyrolysate of the obtained struvite were amorphous magnesium sodium phosphate (MgNaPO₄) and MgO. When the struvite pyrolysate was recycled in the process at the pH range of 8.0-8.5, the precipitation effect was optimum. When the struvite pyrolysate was recycled repeatedly at pH 8.5 or without any adjustment of pH, the outcome of the removal of the nutrients in both cases was similar. With the increase in the number of recycle times, the performance of struvite precipitation progressively decreased. An economic evaluation showed that the combination of using low-cost material and recycling of struvite was feasible. Recycling struvite for three process cycles could save the chemical costs by 81% compared to the use of pure chemicals.     

Recovery of phosphorous from swine wastewater through crystallization

All the phosphate rock Japan needs must be presently imported from abroad because the country has no subterranean phosphorous resources. Therefore, there is a need to accelerate the development of and establish the technologies for phosphorous recovery from waste and wastewater. Swine wastewater has a high potential for phosphorous recovery in Japan. A reactor for removing and recovering phosphorous from swine wastewater was designed with dual functions, crystallization through aeration and separation of formed struvite by settling. However, a dehydration, composting and characterization process was first needed before using sediment sludge, including struvite, on farmland, since the struvite will settle along with huge amounts of other suspended solids (organic matter). For the recovery of pure struvite, an accumulation device was designed and its efficiency examined. The device has a struvite-accumulation face made of stainless steel wire mesh (1 mm in diameter, 1 cm(2) square) to reduce its total weight. During submergence in the aeration column of the demonstration reactor, struvite cross-bridged and accumulated on the face of the device. The struvite could be scraped off easily with only a light brushing, and was found to be approximately 95% pure. Because this device is a very simple structure, it is thought to be acceptable to swine farmers.     

Simultaneous nitrification, denitrification, and phosphorus removal from nutrient-rich industrial wastewater using granular sludge

The biological removal of nitrogen and phosphorus from nutrient-rich abattoir wastewater using granular sludge has been investigated. A lab-scale sequencing batch reactor, seeded with granular sludge developed using synthetic wastewater, was operated for 13 months under alternating anaerobic and aerobic conditions. It is demonstrated that the granules could be sustained and indeed further developed with the use of abattoir wastewater. The organic, nitrogen, and phosphorus loading rates applied were 2.7 gCOD L(-1) day(-1), 0.43 gN L(-1) day(-1), and 0.06 gP L(-1) day(-1), respectively. The removal efficiency of soluble COD, soluble nitrogen and soluble phosphorus were 85%, 93%, and 89%, respectively. However, the high suspended solids in the effluent limited the overall removal efficiency to 68%, 86%, and 74% for total COD, TN, and TP, respectively. This good nutrient removal was achieved through the process known as simultaneous nitrification, denitrification, and phosphorus removal, likely facilitated by the presence of large anoxic zones in the center of the granules. The removal of nitrogen was likely via nitrite optimizing the use of the limited COD available in the wastewater. Accumulibacter spp. were found to be responsible for most of the denitrification, further reducing the COD requirement for nitrogen and phosphorus removal. Mineral precipitation was evaluated and was not found to significantly contribute to the overall nutrient removal. It is also shown that the minimum HRT in a granular sludge system is not governed by the sludge settleability, as is the case with floccular sludge systems, but likely by the limitations associated with the transfer of substrates in granules.     

Removal and recovery of phosphorous from swine wastewater by demonstration crystallization reactor and struvite accumulation device

A demonstration crystallization reactor and struvite accumulation device for the removal and recovery of phosphorous was constructed and their performance was evaluated using actual swine wastewater for 3.5 years. The wastewater pH was increased by aeration, and the concentrations of total P and soluble PO(4)-P were reduced by a struvite crystallization reaction induced under a high pH condition. A 30% MgCl(2) addition was effective in enhancing the struvite crystallization reaction. The concentrations of suspended solids, total Zn and total Cu, were also decreased by the settling function of the reactor. On removing the efficiencies of these components, no noticeable seasonal fluctuation in performance was observed during the 3.5-year operation. In terms of maximum yield, 171g struvite was obtained from 1m(3) swine wastewater by the demonstration accumulation device for struvite recovery. The recovered struvite needed only air-drying before use since it was approximately 95% pure even without washing.     

Incorporation of ultrasonic cell disintegration into a membrane bioreactor for zero sludge production

For the prevention of excess sludge production from a membrane bioreactor (MBR), an ultrasonic cell disintegration process was incorporated. The results of this study showed that excess sludge production could be prevented using an ultrasound hybrid (MBR-US) system at an organic loading of around 0.91 kg BOD₅/m³ per day. Under the same organic loading rate, the mixed liquor suspended solid (MLSS) of MBR-US system was maintained at 7000–8000 mg/l while the MLSS of a conventional MBR increased from 7000 to 13,700 mg/l during the experimental period. While sludge production was completely prevented, the effluent quality of the MBR-US system slightly deteriorated. The additional organic loading caused by disintegrated sludge return was considered to be a reason. With sonication the volume of the average particle size of the sludge in the aeration tank decreased from 132 to 95 μm. In the MBR-US system, around 25–30% of total phosphorus removal was achieved without sludge removal from the aeration tank.     

Optimal production of polyhydroxyalkanoates (PHA) in activated sludge fed by volatile fatty acids (VFAs) generated from alkaline excess sludge fermentation

To reduce the production cost of polyhydroxyalkanoates (PHA) and disposal amount of excess sludge simultaneously, the feasibility of using fermentative volatile fatty acids (VFAs) as carbon sources to synthesize PHA by activated sludge was examined. At pH 11.0, 60 degrees C and fermentative time of 7d, the VFAs yield was 258.65 mgTOC/gVSS. To restrain cell growth during PHA production, the released phosphorus and residual ammonium in the fermentative VFAs was recovered by the formation of struvite precipitation. Acetic acid was the predominant composition of the fermentative VFAs. PHA accumulation in excess sludge occurred feeding by fermentative VFAs with aerobic dynamic feeding process. The maximum PHA content accounted for 56.5% of the dry cell. It can be concluded from this study that the VFAs generated from excess sludge fermentation were a suitable carbon source for PHA production by activated sludge.     

Partial nitrifying granule stimulated by struvite carrier in treating pharmaceutical wastewater

Aerobic granule was successfully cultivated in SBR (sequencing batch reactor) by struvite carrier (magnesium ammonium phosphate, MgNH₄PO₄), which can increase polysaccharides to 42.2 mg/gMLVSS (mixed liquor volatile suspended solid) versus only 28.4 mg/gMLVSS of the sludge without it. Meanwhile, it was found that struvite play a positive role in initial granulation and bacterial group distribution in treating pharmaceutical wastewater, involving effect of solid surface and special contents of struvite. The results of fluorescence in situ hybridization technique indicate that ammonia-oxidizing bacteria can dominate over nitrite-oxidizing bacteria in mature granules. COD removal efficiency of 90 % and NO₂ ^?–N:(NO₂ ^?–N?+?NO₃ ^?–N) accumulation efficiency of 89 % were achieved in stable state. Emphasis is placed on that struvite addition can be applied as a new-type carrier to promote formation of partial nitrification granular sludge.     

不同水肥条件下AM真菌对丹参幼苗生长和营养成分的影响

利用盆栽接种试验,探讨不同水肥条件下AM真菌摩西球囊霉Glomus mosseae对丹参幼苗生长和微量元素的影响,为丹参水肥合理施用提供理论依据。结果表明,不同水肥条件下,接种AM真菌显著提高了根系侵染率和生物量。40%相对含水量、不同施P水平,接种株丹参酮含量升高,总黄酮、丹参素及地下部总酚酸含量降低,植株Zn及地上部Ca、K、Mn、Fe含量升高,而对植株Mg、Cu和地下部Ca、K、Mn、Fe无显著影响;接种效应随施P量不同而变化。70%相对含水量、不同施P水平,接种株药用成分含量显著升高,植株Ca、Mn和地上部K、Cu及地下部Fe和Zn含量升高,而对植株Mg、地下部K、Cu和地上部Fe和Zn含量无显著影响。不同水分和同一施P水平,接种株丹参酮含量升高,地上部Ca、K和地下部Zn含量升高,接种效应因土壤含水量不同而变化,其中以70%含水量时效果最好。说明AM真菌能促进宿主植物根系对水分和矿质元素的吸收与利用,提高水分和P肥利用率,降低水分和P胁迫对丹参的伤害程度,其中以70%相对含水量,施P量为0.16 gP/kg土时AM真菌对丹参的接种效果最佳。     

Some Bag Experiments on Tibbs Run Lake,W.V., A Eutrophic Acidified Lake

Tibbs Run Lake was sampled from December 1979 to December 1980, monthly during the winter and biweekly during the spring, summer, and autumn. Primary production was measured from March 1980 to February 1981, either monthly or biweekly, as indicated above. The mean annual hydrogen ion concentration was equivalent to pH 4.33. This pH was 46% lower (based on H⁺ concentrations) than the 1977–1978 mean. The low pH of the lake is due to inputs of acid precipitation and the low buffering capacity of the watershed. Predictions of further reductions in the lake pH, based on mean annual hydrogen ion concentrations and hydrogen ion retention coefficients (RH) from Shellito (1979) and this study, indicate that the lake pH should reach an equilibrium with the precipitation pH between 1982 and 1985, assuming the precipitation pH continues to average 4.10. The stratified period mean chlorophyll a and total phosphorus concentrations were 22.1 mg/m³ and 19.3 μg/1, respectively. Total phosphorus loading to the lake was 0.233 gP/m²/yr. To examine the effects of neutralization and fertilization with phosphorus an in situ bag enclosure experiment, lasting 16 days, was performed during the summer of 1980. In the bags, phosphorus (20 μg/1 on days 0,4,8,12 as KH₂PO₄) was added alone and in combination with a base addition (IN KOH). The base additions raised the pH to approximately 7.8. Other treatments included base addition alone and a control. The maximum chlorophyll a concentration was found in the phosphorus treatment (∼30 mg/m³) on day 6. The phosphorus plus base treatment exhibited a 10 day lag before reaching a maximum chlorophyll a concentration (∼27 mg/m³) on day 16. The highest production rate was found in the phosphorus plus base treatment on day 12 (∼27 mgC/m³/hr.). A similar bag experiment, lasting 46 days, was performed during the late summer and early autumn of 1980. The treatments were the same as in the first experiment, however, the nitrate-nitrogen depletion in the lake and treatments necessitated the addition of nitrogen (2 mg/1 as NaNO₃) to one of each replicate treatment on day 5. On day 34, the maximum chlorophyll a concentrations were found in the phosphorus plus base nitrogen treatment (∼120 mg/m³) and the phosphorus plus nitrogen treatment (∼38.8 mg/m³). The control plus nitrogen treatment was submerged and possibly contaminated on day 5. All treatments not receiving nitrogen, except for the phosphorus plus base treatment, decreased in the chlorophyll a concentration throughout the experiment. The phosphorus plus base treatment peaked in the chlorophyll a concentration on day 45 (∼28 mg/m³) despite non-detectable levels of nitrate-nitrogen. The maximum primary production rate was found in the phosphorus plus base plus nitrogen treatment (∼32 mgC/m³/hr.) on day 11.     

Struvite precipitation by soil and fresh water bacteria

Struvite precipitation by 161 bacterial strains isolated from soil and fresh water was analyzed. The results showed that the ability to form struvite is not widespread among these bacteria. Struvite precipitation was influenced by environmental factors and could be enhanced by changing the experimental conditions. There was no clear relationship between the taxonomic status of a given strain and its ability to precipitate struvite. However, bacteria of the genusPseudomonas showed a greater tendency to precipitate struvite than organisms of the remaining genera studied, and five new genera were identified as struvite producers.     

不同降水年型下长期施肥旱地小麦产量效应

以黄土高原30年长期肥料定位试验为基础,依据降水将生育年划分为干旱年、平水年和丰水年,研究不同施肥方式对黄土高原冬小麦产量、肥料贡献率和降水利用率的影响.结果表明: 小麦连续种植30年中,氮磷配施和氮磷钾配施下小麦产量、肥料贡献率和降水利用率显著高于不施肥和单施肥处理,氮磷钾配施下小麦产量、肥料贡献率和降水利用率分别达到3480 kg·hm^-2、61.45 kg·kg^-1、6.13 kg·mm^-1·hm^-2;不同降水年型下,丰水年小麦产量、肥料贡献率和降水利用率相对较高;使用逐步回归分析可知,不同降水年型下小麦产量主要受氮磷肥施用量、休闲期降水和越冬期降水影响.黄土旱塬可以通过提高氮磷用量同时适当施用钾肥,以及在休闲期做好蓄水保墒工作来提高小麦产量.     

The phosphorus fractions and alkaline phosphatase activities in sludge

The alkaline phosphatase activities (APA) and phosphorus fractions in activated sludge during wastewater treatment were studied. Our results showed that the phosphorus concentration and fractions in activated sludge were highly correlated with the characteristics of influents. Inorganic phosphorus (IP) and non-apatite inorganic phosphorus (NAIP) were the main phosphorus fractions of sludge. A larger phosphorus concentration was found in activated sludge due to the more readily mobilizable and bio-available forms. The APA in sludge was directly correlated with mixed liquor suspended solids (MLSS) in activated sludge. The APA in the sludge is implicated the depletion of organic phosphorus forms in sludge, whilst also implying its less inhibition of inorganic phosphorus in sludge. The APA and phosphorus fractions in different sludge samples from the same wastewater treatment plant were quite stable. This stability shows their tight interactions in sludge.     

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.     

Control of struvite precipitation by selective removal of $${\text{NH}}^{{\text{ + }}}_{{\text{4}}} $$ with dialyzer/zeolite in an anaerobic membrane bioreactor

This study focused on the mitigation of membrane fouling caused by struvite precipitation using a dialyzer/zeolite (D/Z) unit in an anaerobic membrane bioreactor. The D/Z unit was designed to selectively remove NH(4)+ ions, one of the main components of the inorganic foulant, struvite. The maximum mass transfer coefficient for NH(4)+ through the dialyzer was estimated to be 0.92 l m(-2)h(-1), whereas the Na-substituted zeolite had the highest ion exchange capacity with respect to ammonium among intact or differently pretreated zeolites. During a single passage of dialysate through the zeolite column, substantial NH(4)+ removal (in excess of 90%) was achieved, leading to the reduction in struvite precipitation in the digester. The D/Z unit played a significant role in controlling struvite precipitation, thereby enhancing permeate flux for the case of the ceramic membrane, in which struvite fouling would be more pronounced compared to the polymeric membrane. For the polymeric membrane, however, no significant improvement in flux was observed even with the D/Z unit because the fouling of the polymeric membrane was mainly due to the deposition of biomass rather than the struvite precipitation.     

Bio-Acidification and Leaching of Metals,Nitrogen, and Phosphorus from Soil and Sludge Mixtures

Soil and wastewater treatment sludge are commonly brought together in mixtures for a variety of beneficial purposes. The mixtures contain bioacidifying (i.e., sulfur-oxidizing) microorganisms that can easily be activated through providing the appropriate substrate and environmental conditions. In this study, contaminated soil and sludge mixtures were subjected to controlled bio-acidification and the impacts of the process on the partitioning of heavy metals, nitrogen, and phosphorus were examined. Three successive bio-acidification cycles resulted in significant leaching of metals from sludge. The leaching results, expressed as fraction of total mass of metals in the sludge, averaged 67% for Cr, 96% for Ni, 24% for Zn; 16% for Cu; 23% for Cd; and 96% for Pb. Bio-acidification of the sludge also converted 28 to 45% of the organic nitrogen into ammonia and increased the soluble orthophosphates fraction of total phosphorus by approximately 18 to 20%. Bio-acidification also resulted in significant metals leaching from the contaminated soils in the soil/sludge mixtures. Soil/sludge mixtures were prepared using six soil particle sizes (less than 0.075?mm to 2.38?mm) contaminated with 22,500?mg/kg Zn, 14,000?mg/kg Pb, 1500?mg/kg Cr, 9500?mg/kg Cu, 1000?mg/kg Ni, and 1000?mg/kg Cd. The addition of metals to the soil inhibited the sulfur-oxidizing microorganisms, preventing bio-acidification in the mixtures containing 4 to 50?g soil in 130?ml sludge, and considerably slowing bio-acidification in the mixtures containing 1 to 3?g soil. Using a mixture that contained 2-g soil samples, three successive bio-acidification cycles resulted in significant cumulative metals leaching results. The leaching results, expressed as percentage of the mass of metals added to the soil, were in the range of 56 to 98% for Cr, 77 to 95% for Zn, 33 to 66% for Ni, 64 to 82% for Cu, and 10 to 33% for Pb, with the higher results in each range belonging to the larger size soil particles. On the other hand, only Cr was leached in neutralized soil samples. The results confirmed the potential for inhibition of the sulfur-oxidizing microorganisms and bio-acidification in contaminated soil/sludge mixtures, and the significant impacts of bio-acidification on the mobility of metals, nitrogen, and phosphorus. In addition, the results confirmed the potential for using controlled bioacidification for removing heavy metals from contaminated soil using the indigenous sulfur oxidizing microorganisms in sludge.     

Protein recovery from excess sludge for its use as animal feed

In this study, the possibility of using proteins recovered from excess sludge as animal feed was investigated. The proteins were recovered through the processes of sludge disintegration (alkali treatment followed by ultra-sonication), precipitation and drying of the soluble proteins. The compositions and the toxicants of the recovered proteins were analyzed, and the toxicity was assessed by Sprague-Dawley (SD) rat experiments. The results showed that the nutrient compositions were comparable with the commercial protein feeds. Heavy metals were found to be removed after the protein recovery process, and aflatoxin B1, ochratoxin A and Salmonella D groups were not detected. The rat toxicity tests showed that there were no effects on mortality, the incidence of clinical signs, body weight changes, and necropsy findings. The minimum lethal dose (MLD) was higher than 2000mg/kg. Based on these results, the use of the crude protein recovered from excess sludge as animal feed appears to be technically feasible.