In this study, molecular community analysis and analytical measurements were combined to assess and compare the identity, functionality, structure, and temporal changes of membrane and conventional enhanced biological phosphorous removal systems (which ran stable over 300 days) and to identify the dynamics of the foam forming population. Magnesium was added to the system with the goal to enhance phosphate removal. Both systems behaved similarly with respect to phosphate and nitrogen removal efficiency and had similar community evenness, but they differed in community composition. A principle component analysis indicated that, the community of the membrane system changed permanently whereas the conventional system returned to approximately its initial composition. The relative intensity of DGGE bands were transformed in a numerical matrix and based on this matrix a model was constructed, which predicted some bands as foam forming bands, which were identified as foam‐forming filamentous bacteria by sequencing.

The research and development work on nutrient recovery from wastewater streams, currently being carried out by the authors, is outlined. The potential of phosphorus, nitrogen and potassium recovery using crystallisation of struvite-type compounds is discussed. The full, pilot and bench-scale processes demonstrate the large potential of struvite-based nutrient recovery technologies, provided that the process background is thoroughly investigated and the proper process design is in place. The crystallisation of these compounds from wastewater offers an excellent opportunity for nutrient recovery and reuse; wastewater streams from different sources, therefore, must be considered as a valuable resource.

The feasibility of stripping CO2 from anaerobic digester centrate (generated in a sludge dewatering process) to raise pH, and therefore reduce the cost of caustic chemical(s) dosage for similar operation in a struvite-recovery system, was investigated. A cascade CO2 stripper was installed in a pilot-scale, struvite-recovery reactor system at the Lulu Island Wastewater Treatment Plant, Richmond, British Columbia, Canada, as a replacement of part of (about 1/3) the reactor downpipe. Centrate was used as the process feed. Both the influent and the effluent from the struvite reactor were analyzed for pH, temperature (°C), and concentrations of Mg, NH4-N, and PO4-P. Results indicated that, by adding the CO2 stripper, caustic chemical savings was as much as 46% – 65%. Moreover, because of the capability of the stripper in providing a more gradual pH increase, fewer fine solids were produced in the reactor than when caustic solution was used to raise the pH of the reactor.

The feasibility of stripping CO2 from anaerobic digester centrate (generated in a sludge dewatering process) to raise pH, and therefore reduce the cost of caustic chemical(s) dosage for similar operation in a struvite-recovery system, was investigated. A cascade CO2 stripper was installed in a pilot-scale, struvite-recovery reactor system at the Lulu Island Wastewater Treatment Plant, Richmond, British Columbia, Canada, as a replacement of part of (about 1/3) the reactor downpipe. Centrate was used as the process feed. Both the influent and the effluent from the struvite reactor were analyzed for pH, temperature (°C), and concentrations of Mg, NH4-N, and PO4-P. Results indicated that, by adding the CO2 stripper, caustic chemical savings was as much as 46%–65%. Moreover, because of the capability of the stripper in providing a more gradual pH increase, fewer fine solids were produced in the reactor than when caustic solution was used to raise the pH of the reactor.

Struvite, a crystalline structure comprised of ions of magnesium (Mg+2), ammonium (NH4-N), and phosphate (PO4-P), is commonly encountered in wastewater treatment plants (WWTPs) through struvite encrustation. The gradual accumulation of this crystal in pipes and fittings leads to high costs due to downtime and replacement of parts. Technologies that are used to reduce this problem are ideally located in biological nutrient removal plants downstream of anaerobic digesters, as high levels of NH4-N and PO4-P typically characterize anaerobic digester supernatants. In 2003-2004, two technical-scale, struvite recovery studies were conducted on-site at the City of Penticton, B.C., Canada and the City of Richmond, B.C., Canada using a novel technology developed by the environmental engineering group at the University of British Columbia. The results of these studies showed an average reduction of 80% in phosphate and a dense, spherical product, 5-10 times larger than any commercially available struvite to date. Overall, the recovery of struvite has enormous commercial potential, which results in WWTP becoming more sustainable, concurrently reducing problems typically associated with their operation.

One of the major operational costs of phosphorus recovery as struvite is the cost of caustic chemical that is added to maintain a desired level of operative pH. A study was conducted at the Lulu Island Wastewater Treatment Plant (LIWWTP), Richmond, BC, using a struvite crystallizer and a cascade stripper designed at the University of British Columbia (UBC). The stripper was tested under different operating conditions to determine the effectiveness of CO(2) stripping in increasing the pH of the water matrix and thereby reducing caustic chemical use. This reduction is expected to reduce the operational costs of struvite production. Throughout the project, a high percentage (90%) of phosphorus removal was achieved under each condition. The cascade stripper was very effective in saving caustic usage, ranging from 35% to 86%, depending on the operating conditions. However, the stripper showed relatively poor performance regarding ammonia stripping.

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.

This research investigated the feasibility of stripping CO2 from the digester supernatant to raise the pH, thereby reducing the caustic chemical usage. In this study, a cascade CO2 stripper was first designed and tested, with three different synthetic solutions in a struvite recovery, crystal reactor: (1) tap water saturated with CO2, (2) NaHCO3 solution saturated with CO2, and (3) NaHCO3 + NH4Cl solution saturated with CO2. It was found that the removal efficiency of the CO2 stripper was dependant on several parameters, such as the characteristics of the influent, including total alkalinity, temperature, and initial concentration of dissolved CO2 gas, influent flow rate, effluent recycle rate, aeration rate, and baffle numbers in the stripper. Based on the performance of the stripper on the three synthetic solutions, a CO2 stripping model was developed using these parameters. This model was subsequently tested in a pilot-scale facility, to predict the amount of CO2 removal possible.

Struvite, a crystalline structure comprised of ions of magnesium (Mg2+), ammonium (NH4-N) and phosphate (PO 47 P),is commonly encountered in wastewater treatment plants (WWTPS) through struvite encrustation. The gradual growth of this crystal can lead to high maintenance costs, due to downtime and replacement parts. Several struvite recovery unit processes have been developed in an effort to reduce this problem, through the preferential removal of the constituent ions (Mg2+, NH4-N, and PO4-P) upstream of problem areas (e.g. anaerobic digester supernatants). One of the key elements of process control for these systems is accurately determining the constituent concentrations. Although a wide variety of measurement techniques exist for both NH4-N and PO4-P, the presence of PO4-P interferes with the measurement of Mg2+. Ion selective electrodes (ISEs) were tested on wastewater samples to determine Mg2+ concentrations. It was found that the two ISE tested produced unreliable results, as they both proved non-specific to Mg2+. A modification, using polyaluminum chloride (PAC), was developed to remove the interference of phosphates from the colorimetric technique. It was found to produce reliable results within 10% of those results predicted by atomic absorption. The resulting technique averaged about 10 minutes per sample and could be conducted inexpensively at a laboratory facility at WWTPs.

The performance of a pilot-scale, struvite crystallization process, for recovering phosphorus from various supernatants, was investigated. Using synthetic supernatant, as well as anaerobic digester supernatants from two full-scale wastewater treatment plants located in Vancouver, B.C., Canada, it was found that over 90% phosphate removal efficiency was achieved through controlling the supersaturation ratio, operational pH and magnesium dosage in the supernatant. With a high supersaturation ratio, or high operational pH, or high magnesium dosage, excellent phosphate removal was achieved. However, an operational pH greater than 8 was not necessary;; it was possible to control the process using a high magnesium dosage in place of a higher operating pH, but without a compromise in phosphate removal. Chemical analysis of the harvested crystals indicated very pure struvite (in excess of 91%), with only small amounts of residual calcium, carbonate, and trace metals. Most crystals exceeded 2 mm in mean diameter.

Intentional crystallization of struvite, before it forms and accumulates on wastewater treatment equipment, solves an important and costly wastewater treatment problem and on the other hand, provides an environmentally sound and renewable nutrient source to the agricultural industry. Struvite was synthesized in the laboratory; it was also produced as pellets in a pilot-scale, fluidized bed reactor, using real centrate resulting from an anaerobic digester. The thermal decomposition of both synthetic struvite and struvite pellets was studied. The decomposition of struvite was found to be dependent on the rate of heating. Through gradual loss of ammonia and water molecules, ultimately struvite was found to be transformed into amorphous magnesium hydrogen phosphate. When struvite was heated in excess water, it was partially transformed into bobierrite, through the gradual loss of ammonia. It was transformed into monohydrate, dittmarite by losing its five water molecules of crystallization, when boiled in excess water.

The solubility of magnesium ammonium phosphate hexahydrate (struvite) was determined in different water and wastewater solutions, by using the analytical results of the solubility tests conducted in the Environmental Engineering Lab at the University of British Columbia. The various factors affecting the struvite solubility such as pH, ionic strength and the temperature of the solutions were also studied in this project. The struvite solubility product values were found to vary significantly from one solution to another and over the range of the experimental conditions as well. For instance, the solubility product (K,) determined at 20 degrees C for anaerobic digester supernatant from the Penticton, B.C. Advanced Wastewater Treatment Plant, was found to vary from 8.46 x 10(-15) (pK(sp) = 14.07) to 1.3 x 10(-13) (pK(sp) = 12.89), over a PH range of 6.45 to 8.97, while in the case of distilled water, with the same struvite crystals and at the identical temperature, it was found to vary from 5.21 x 10(15) (pK(sp) =14.28) to 2.12 x 10(-13) (pK(sp) =12.67) over a pH range of 7.01 to 9.62. These results explore the possible reasons for widely varying struvite solubility reported in the literature. A possible correlation was also developed to correlate struvite solubility product with varying temperature. Furthermore, an attempt was made to establish a correlation between conductivity and calculated ionic strength of the solutions. A significant gap, between the values predicted by the correlation developed in this study and those predicted by the existing correlation, was also observed.

Thick (1500 to 2500 A) NaCl films were formed under ultra high vacuum (UHV) conditions on aircleaved mica substrates at 25, 100, 150, 200, 250, 300 and 380°C by vacuum deposition. A modified version of a UHV reflection high energy electron diffraction (RHEED) camera, designed and constructed in our laboratory was used for these studies. Typical residual gas pressures after bakeout were in the low 10-10 torr range. The aircleaved muscovite mica substrate was clamped to an OFHC copper block about 10 cm. from the resistance heated vapor source. The substrate was outgassed in UHV at 400 C for a period of at least 12 hours before cooling to the deposition temperature. During deposition the pressure was kept in the 10-9 torr range. The film was examined first in situ by the UHV RHEED technique and then replicated. Finally the system was opened and the Ge-SiO replicas mounted on Cu grids and examined by transmission electron microscopy.