Nutrient removal from UASB effluent in agro-industries

Phosphorus and nitrogen are important elements, making a major contribution to agricultural and industrial development, but their release to natural water bodies are the main causes of eutrophication. Anaerobic digestion yields effluents rich in ammonium and phosphate and poor in biodegradable organic carbon, thereby making them less suitable for conventional biological nitrogen and phosphorus removal. In addition, the demand for fertilizers is increasing, energy prices are rising and global phosphate reserves are declining. This requires both changes in wastewater treatment technologies and implementation of new processes. In this contribution the combination of an ureolytic MAP (magnesium ammonium phosphate) precipitation and autotrophic nitrogen removal is described on the anaerobic effluent of a potato processing company to obtain a more sustainable and cheaper method than conventional wastewater treatment processes. The results obtained during this experiment (6 weeks period) show that it is possible to recover phosphate as struvite and remove nitrogen with the autotrophic nitrogen process from wastewater after anaerobic digestion coming from a potato processing company. However further research is necessary to obtain stable results during several months, especially for the nitrite:ammonium ratio produced by the partial nitritation reactor

Economic evaluation of the precipitation of phosphate as struvite at pilotscale

A novel approach using ureolytic induced MAP formation, for the recovery of phosphate, has been economically evaluated. The ureolytic MAP crystallizationon has been tested on anaerobic effluent of a potato processing company in a pilot plant, with MgCl2.6H2O as magnesium source. The pilot plant showed a high phosphate removal efficiency of 82 ± 9 %, resulting in a final effluent concentration of 13 ± 7 mg/L PO4-P. XRD analyses confirmed the presence of struvite in the precipitate. During operation pH and the molar magnesium : ammonium : phosphate ratio are the most important operational parameters influencing MAP crystallization. Results show that for high phosphate concentrations in wastewater (e.g. 100 mg/L PO4-P) the ureolytic phosphate precipitation is a cost effective method (6.1 € kg-1 Premoved). Moreover, the technique is competitive with the chemical phosphate precipitation of struvite (6.2 € kg-1 Premoved)

'One reactor' autotrophic nitrogen removal after ureolytic phosphate precipitation to remove both endogenous and exogenous nitrogen

Nowadays, anaerobic digestion plants are being developed that minimize energy consumption, CO2 emission and sludge production. However, these systems typically yield effluents rich in ammonium and phosphate and poor in biodegradable organic carbon, thereby making them less suitable for conventional biological N- and P- removal. Global phosphate reserves are declining and occur exclusively as phosphate ore. Through an increasing reliance of many industries on phosphate, there is a growing necessity for sustainable phosphate management. Phosphate recovery as struvite or magnesium ammonium phosphate (MAP) is becoming an important issue because it permits phosphate recycling in the fertilizer industry since struvite is known as a slow release fertilizer. Ureolytic phosphate precipitation (UPP) is a new method for phosphate removal which however introduces extra ammonium in the system. The Autotrophic Nitrogen Removal (ANR) process, a new and alternative method for nitrogen removal, consumes 63% less oxygen and 100% less biodegradable organic carbon when compared to the conventional nitrification and denitrification process and therefore has a lower operating cost. The combination of anaerobic digestion, ureolytic phosphate recovery by precipitation as struvite and nitrogen removal with the ANR process is proposed as a more sustainable and cheaper method than conventional wastewater treatment processes in which phosphate is not recuperated. In this contribution we investigate the removal of both the endogenous ammonium in the effluent of an USAB of a potato processing company and the ammonium derived from the ureolytic phosphate precipitation. The Autotrophic Nitrogen Removal process was tested in a one reactor system also known as the OLAND (Oxygen Limited Autotrophic Nitrification Denitrification) process

'A Single reactor' Autotrophic Nitrogen Removal Process after Ureolytic Phosphate Precipitation to remove both endogenous and exogenous nitrogen

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Ureolytic phophate precipitation from wastewater

MAPLE and PHREEQC were used for modelling phosphate precipitation from waste-water as struvite. Our simulations showed that relative high concentrations of ammonium and magnesium ions are necessary to precipitate the phosphate as struvite: to reduce phosphate-P con-centration from 20 to 6 ppm relative concentrations of Mg2+, phosphate-P and NH4+ of 4.6/1/8 are necessary. An ureolytic method previously developed for the precipitation of calcium-ions from wastewater as calcite, was adapted to the precipitation of phosphate as struvite. When a synthetic wastewater or wastewater from a vegetable processing company, urea and a source of magnesium ions were added to ureolytic sludge, struvite was formed; meanwhile the phosphate concentration of the wastewaters decreased and pH increased to about 8.5. Using a continuous reactor with a hydraulic retention time of 2.4 h and relative molar excesses of 4.6 and 2.6 to phosphate of magnesium ions and urea respectively it was possible to decrease the phosphate concentration from 30 to 4 ppm phosphate-P. The reactor worked relatively stable under a broad range of experimental conditions.status: publishe

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 (R) 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 PO4-P. Calculating the evolution of the saturation index (SI) as a function of the remaining concentrations of Mg2+, PO4-P and NH4+ during precipitation in a batch reactor, resulted in a good estimation of the effluent PO4-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 PO4-P) was calculated as 3.9 (sic) 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 (R) technology in terms of operational cost and removal efficiency but further research is necessary to obtain larger crystals

Recovery of nutrients from wastewater: a market for artificial manure?

Phosphorus and nitrogen are important elements, making a major contribution to agricultural and industrial development, but their release to natural water bodies are the main causes of eutrophication. In addition, the demand for fertilizers is increasing, energy prices are rising and global phosphate reserves are declining. Meaning that besides meeting the nutrient standards, nutrient removal should be replaced by nutrient recovery. This requires both changes in wastewater treatment technologies and implementation of new processes. Also the commercializing and potential users for the recuperated nutrients making part of these changes. For the recovery of phosphorus (as phosphate) the application of a struvite precipitation process in a WWTP is beneficial to reduce the consumption of phosphate rocks, and to obtain a recovered product that can be used as a fertilizer or used as raw material in the phosphorus industry. Currently, only few full-scale struvite crystallization plants exist. This is due to the lack of information about the benefits of struvite as a fertilizer, its value on the market, and problems related to the crystallization process. Nitrogen in current WWTP is removed by nitrification-denitrification. The nitrogen (as nitrate), that remains in the wastewater after anaerobic digestion and struvite precipitation could be recovered in the brine that results after the treatment of this wastewater with a membrane bioreactor and reverse osmosis. In this study we want to find the potential users and markets of these “natural stable fertilizers” (struvite and the brine) in Belgium or abroad

Autotrophic nitrogen removal after ureolytic phosphate precipitation to remove both endogenous and exogenous nitrogen

Anaerobic digestion yields effluents rich in ammonium and phosphate and poor in biodegradable organic carbon, thereby making them less suitable for conventional biological nitrogen and phosphorus removal. In addition, the demand for fertilizers is increasing, energy prices are rising and global phosphate reserves are declining. This requires both changes in wastewater treatment technologies and implementation of new processes. In this contribution a description is given of the combination of a ureolytic phosphate precipitation (UPP) and an autotrophic nitrogen removal (ANR) process on the anaerobic effluent of a potato processing company. The results obtained show that it is possible to recover phosphate as struvite and to remove the nitrogen with the ANR process. The ANR process was performed in either one or two reactors (partial nitritation + Anammox). The one-reactor configuration operated stably when the dissolved oxygen was kept between 0.1 and 0.35 mg L-1. The best results for the two-reactor system were obtained when part of the effluent of the UPP was fully nitrified in a nitritation reactor and mixed in a 3: 5 volumetric ratio with untreated ammonium-containing effluent. A phosphate and nitrogen removal efficiency of respectively 83 +/- 1% and of 86 +/- 7% was observed during this experiment

Ureolytic phosphate precipitation from anaerobic effluents

In this work, the elimination of phosphate from industrial anaerobic effluents was evaluated at lab-scale. For that purpose, the ureolytic method previously developed for the precipitation of Ca2+ from wastewater as calcite was adapted for the precipitation of phosphate as struvite. In the first part of the study, computer simulations using MAPLE and PHREEQC were performed to model phosphate precipitation from wastewater as struvite. The results obtained showed that relative high concentrations of ammonium and magnesium are needed to precipitate phosphate as struvite. The total molar concentrations ratio of Mg2+: PO43--P:NH4+ required to decrease PO43--P concentrations from 20 to 6mg PO43--P/l at pH 8.4-8.5 was estimated on 4.6:1:8. In the second part of the study, lab-scale experiments with either synthetic wastewater or the anaerobic effluent from a vegetable processing industry were carried out in batch and continuous mode. Overall, the continuous operation at a hydraulic retention time (HRT) of 2.4 h and an added molar concentration [Mg2+]:[PO43 -P]:[ NH4+] ratio of 1.6:1:2.3 resulted in a constant pH value in the reactor (around 8.5) and an efficient phosphate removal (>90%) to residual levels of 1-2 mg PO43--P/l. Different operational conditions, such as the initial phosphate concentration, HRT and the use of CaCl2 or MgO instead of MgCl2, were analysed and the performance of the reactor was satisfactory under a broad range of them. Yet, overall, optimal results (higher phosphate removal) were obtained with MgCl2