P removal from anaerobic supernatants by struvite crystallization: long term validation and process modelling

Battistoni, P.; Angelis, Anna De; Prisciandaro, Marina; Boccadoro, R.; Bolzonella, David

doi:10.1016/s0043-1354(01)00401-8

Cited by 87 publications

(59 citation statements)

References 13 publications

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“…Crystallization is initiated by nuclei, which may be grains of sand, or by contributing energy to the nucleation process by using rakes (Battistoni et al, 2002). In most slurries, the amount of sand is generally high and one would not anticipate any need to enhance the nucleation process.…”

Section: Operation and Separation Efficiencymentioning

confidence: 99%

Solid—liquid separation of animal slurry in theory and practice. A review

Hjorth

Christensen

et al. 2010

Agron. Sustain. Dev.

338

235

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-Animal slurry contains plant nutrients that are essential for crop production. However, intensive livestock production may lead to a surplus of plant nutrients on farms and, as a consequence, discharge or emission to the environment. In order to ensure that the slurry applied to fields matches the nutrient requirements of the crops, techniques have been developed to reduce the nutrient content of slurry by means of separation. This review discusses the separation technologies used for animal slurry treatment and the physical and chemical processes involved in separation. These processes need to be understood before efficient, reliable and cheap separation technologies that take into account the actual properties of slurry and the likely end-use of the separation products can be developed. A simple separation efficiency expression can be used to assess the efficiency of slurry separation. It is indeed important to measure the amount and composition of the slurry before treatment, the dry-matter-rich fraction and the liquid fraction. The separation efficiency of mechanical separators for the removal of dry matter and phosphorus (P) is ranked as follows: centrifugation > sedimentation > non-pressurized filtration > pressurized filtration. In general, the separation of total N and NH + 4 follows the same pattern, but the separation efficiency is lower than for dry matter and P. Treatment with a flocculant before separation improves separation efficiency significantly. Of the polyacrylamide polymers tested, high-molecular-weight, linear cationic polymers with a medium charge density (20-40 mol%) were found to be the most efficient flocculants. The best mechanical separation techniques for flocculated slurry are screens or filter belts. The separation efficiency of polyacrylamide-treated slurry can be improved by adding a multivalent ion to coagulate particles and for precipitation of phosphorus. Aluminium sulfate (Al 2 (SO 4 ) 3 ) or ferric chloride (FeCl 3 ) seem to be very efficient for improving the mechanical separators. Alternatively, the mineral struvite (MgNH 4 PO 4 ) may be formed by changing the slurry characteristics, such as by the addition of magnesium (Mg) or by increasing the pH to 9. The struvite crystals are removed during solid-liquid separation. The products of the solid-liquid separation may be further treated by evaporation, membrane filtration or ammonia stripping in order to obtain the desired end-products; however, low-maintenance and/or cost-efficient operation of these post-treatments has not yet been demonstrated. The separation should be developed as a whole-system approach, paying attention to parameters such as the value of end-products, environmental consequences and economy.

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Section: Operation and Separation Efficiencymentioning

confidence: 99%

Solid—liquid separation of animal slurry in theory and practice. A review

Hjorth

Christensen

et al. 2010

Agron. Sustain. Dev.

338

235

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“…The reactor was fed with filtrate from the sludge dewatering system and operated at four different HRTs: 120, 60, 30, and 15 min, and four different aeration rates: 11.2, 24.3, 37.4, and 46.7 m 3 air/h/m 3 reactor, for pH increase. The previous operational parameters were chosen based on results observed by others [12,17] and in order to attain pH in the reactor around pH 8.0 (the minimal theoretical pH to obtain considerably high struvite precipitation). Reactor stirring was accomplished through a Heidolph stirring machine, type RZR1, operated at 240 rpm.…”

Section: Reactor Set-up and Operationmentioning

confidence: 99%

“…Battistoni et al [12]. investigated a laboratory fluidized bed reactor fed with supernatant from a sludge centrifugation system and operated at different air flows, influent concentrations, and retention times (52-177 min).…”

mentioning

confidence: 99%

Controlled struvite precipitation from belt press filtrate of anaerobic digester in a CSTR

Lew

Phalah

Rebhum

2011

Env Prog and Sustain Energy

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Struvite (MgNH 4 PO 4 Á6H 2 O) is known to precipitate and clog pipes and pumps, causing operational difficulties and expenses downstream of the anaerobic digester in wastewater treatment plants around the world. This work focused on determining the most appropriate reactor operational conditions (focus on hydraulic retention time and aeration rate) required for attaining the most homogeneous controlled struvite precipitation in order to reduce pipes and pumps clogging downstream of the digester. To this end a continuous laboratory-scale completely stirred tank reactor aerated (for CO 2 stripping) reactor was operated at different hydraulic retention times and aeration rates and precipitate composition was determined. A minimum pH of 8.0 was calculated and experimental observed as necessary to attain struvite precipitation to its maximum potential to prevent clogging. To reach this pH value a minimum HRT of 0.5 hours with aeration flow rate of 11.2 m 3 /h/m 3 and/or 15-min HRT with an air flow of 46.7 m 3 /h/ m 3 was necessary for the reactor studied. Struvite precipitation kinetics was observed to be much faster than other minerals that can precipitate and a decrease in HRT promoted a precipitate richer in struvite. However, for all HRT and air flows studied the precipitate obtained can be considered to be poor in struvite and can hardly be reused in agriculture.

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“…Dissolved and ionic species present in the system are NH 3 7. Activity coefficients were assumed to be unity.…”

Section: Assumptionsmentioning

confidence: 99%

“…These models are based on physicochemical equilibrium of the various ionic, dissolved, and solid species. A struvite precipitation model at least requires the incorporation of concentrations of ionic species NH 4 + , PO 4 3− , and Mg 2+ , dissolved species NH 3 and H 3 PO 4 , and solid species MgNH 4 PO 4 . However, a number of other ionic species (e.g., HPO 4 2− , H 2 PO 4 2− , MgOH + , MgPO 4 − , MgH 2 PO 4 + ), dissolved species (e.g., H 3 PO 4 , MgHPO 4(dissolved) ), and solid species (e.g., Mg 3 (PO 4 [18] did not explicitly determine the concentrations of dissolved, ionic, and solid species but compiled operating curves that related pH with total concentrations of magnesium, nitrogen, and phosphorus in liquid under struvite recovery conditions.…”

Section: Introductionmentioning

confidence: 99%

Validation and Applications of a Chemical Equilibrium Model for Struvite Precipitation

Gadekar

Pullammanappallil

2009

Environ Model Assess

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Removal of nutrients like nitrogen and phosphorus from wastewater can be accomplished by precipitating these as the mineral struvite (NH 4 MgPO 4 . 6H 2 O). Predicting struvite precipitation potential, yield, and purity is important for designers and operators of reactors for struvite precipitation. In this paper, a mathematical model of this precipitation process is developed using physicochemical equilibrium expressions, mass balance equations for nitrogen, phosphorous and magnesium, and charge balance. The model was simulated to explicitly solve for equilibrium concentrations of eighteen species that included dissolved (three), ionic (ten), and solid (five) species for a given set of initial concentrations of ammonium-nitrogen, magnesium and phosphate-phosphorus, and pH. The model simulations were validated against literature experimental data, which used synthetic as well as actual wastewater, and data from our experiments. The model satisfactorily predicted most data. Struvite fraction in the precipitate ranged from 27% to 100%. The purity of struvite in the precipitate and the pH that maximizes struvite fraction was dependent on the initial concentrations of ammonium, magnesium, and phosphate. Optimum pH and struvite fraction was, respectively, 8.5 and 29.3% for an equimolar mixture of ammonia, magnesium, and phosphate and 9.8 and 98.3% for 10:1.7:3.4 mM ratio. Struvite fraction in the precipitate increased as magnesium became limiting or as ammonia to phosphate ratio increased and magnesium to phosphate ratio decreased. Since the struvite component is only a fraction of the total solids, it is erroneous to report the total precipitate produced as being struvite as is conventionally done.

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P removal from anaerobic supernatants by struvite crystallization: long term validation and process modelling

Cited by 87 publications

References 13 publications

Solid—liquid separation of animal slurry in theory and practice. A review

Solid—liquid separation of animal slurry in theory and practice. A review

Controlled struvite precipitation from belt press filtrate of anaerobic digester in a CSTR

Validation and Applications of a Chemical Equilibrium Model for Struvite Precipitation

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