Kazi P. Fattah

Determining the feasibility of phosphorus recovery as struvite from filter press centrate in a secondary wastewater treatment plant

In this study, the workability of a pilot-scale, fluidized reactor was examined to determine effectiveness in removing, and recovering, phosphorus as struvite, from centrate at Lulu Island Wastewater Treatment Plant (LIWWTP), Richmond, British Columbia. The crystallization process was run continuously over a period of 5 months in two runs (Run 1 for 4 months and Run 2 for a month). In addition to efficient recovery of phosphorus as struvite, the study also investigated factors that affect the growth of struvite. Chemical analyses were conducted on the harvested struvite to determine its purity. Results showed that the reactor was capable of removing over 90% of phosphate and 4% of ammonia-nitrogen, with greater than 85% of the phosphate removed being recovered as harvestable struvite crystals. It was possible to achieve over 90% P-removal at a pH of 7.5; this is contrary to the information found in literature, which recommends that a higher pH (8.2–9.0) is required. Factors that affected phosphate removal were the operating pH, the reactor supersaturation ratio (SSR), the N:P and Mg:P molar ratios. Analysis of the harvested product showed that the crystals were composed of nearly pure struvite (96% by weight), with small amounts of calcium and traces of other metals. High resolution SEM pictures were taken of the inside of the crystals to determine the influence of Mg:P molar ratio on the compactness of the crystals.

Influence of Process Parameters on the Characteristics of Struvite Pellets

AbstractWith an ever-increasing demand for phosphate-based fertilizer, new sustainable sources of phosphorus are warranted. Recent technologies have successfully demonstrated the possibility of recovering phosphorus from wastewater-treatment plants as struvite, which is also a ready-made, slow-release fertilizer. However, process parameters that influence the operation of crystallizers and production of good-quality struvite pellets have yet to be fully understood. This paper discusses the influence of process parameters on the characteristics of struvite pellets. Among the various process parameters, upflow velocity and flow patterns in the crystallizer were found to influence the size and shape of the pellets. In the range (1.5–7.1) tested, supersaturation ratio did not appear to influence the crushing strength of the pellets formed. Midsized pellets, in the 2.0–2.5-mm range, exhibited the highest crushing strengths. Higher magnesium concentration in the crystallizer was able to increase the crushing st...

Reducing operating costs for struvite formation with a carbon dioxide stripper.

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.

Designing constructed wetlands for reclamation of pretreated wastewater and stormwater

Wastewater reclamation is getting greater attention as an alternative to conventional approaches to wastewater treatment and water supply due to increasing water stress coupled with more stringent water quality limitation for discharge of treated wastewater. Among the few technologies adopted in the field for wastewater reclamation, constructed wetlands have been used to reclaim both primary and secondary treated wastewater in regions with arid and humid climates. This paper summarizes the widely adopted guidelines that need to be considered when designing constructed wetlands for wastewater reclamation, discusses the capacity of wetland treatment systems for water reuse while assessing the status of full-scale constructed wetlands designed for wastewater reclamation, and develops contaminant loading charts as a design tool based on the performance of existing full-scale constructed wetlands deployed for wastewater reclamation. It is evident that constructed wetland systems provide a viable means to treat wastewater to the levels required for low-quality reuses such as restricted irrigation and impoundment. It is challenging for constructed wetlands to consistently meet microbiological guidelines for high-quality reuses such as unrestricted agricultural and urban reuses. Wastewater reclaimed through constructed wetlands is used mainly for agricultural and landscape irrigation, groundwater recharge, indirect potable reuse, and environmental reuse. Surface area and hydraulic loading rate of constructed wetlands to be deployed for wastewater reclamation can be estimated with contaminant loading charts derived from monitoring data of existing full-scale operations.

Application of artificial neural networks to effluent phosphate prediction in struvite recovery

In advanced wastewater treatment plants (AWWTP), the recovery of phosphorus (P) has become a recent focus of the wastewater engineering industry. The potential economic savings behind improved sludge management and the control of struvite encrustation in AWWTP are two of the primary driving forces behind this. Process control of phosphorus (struvite) recovery systems has only been partially successful because: (1) key control variables have yet to be identified and (2) there is no adequate performance evaluation model that is applicable to struvite recovery technologies. In process control, two different types of modeling are most commonly seen: mechanistic and “black-box” style models. In recent years, varying models have been developed to try to predict the formation of struvite in both sludge digestion process lines and P-recovery technologies designed for struvite removal. All of these are strictly mechanistic models, based on either the chemical equilibrium of the system or the associated kinetic par...

Investigating techniques to determine magnesium addition requirements for the operation of a struvite crystallization process

The recovery of phosphorus from wastewater has gathered strength due to its acceptance as a sustainable method for solving wastewater treatment plant struvite problems and the low global reserves of phosphorus ore. Although the chemistry and successful operation of phosphorus recovery plants are well documented, there still exists opportunity to reduce and optimize the use of external resources, such as magnesium, that is required for the nutrient recovery. One of the primary operational costs arises from the need for external magnesium addition, and therefore, the proper (and timely) detection of the element is necessary. In this study, methods were tested which could provide information, on-site, on the rate of application of the element and its concentration in the various water matrices. A method was developed that utilizes the combined use of pH and conductivity to determine the amount of external magnesium that needs to be added to a water sample. The amount required was determined by locating a transition point in the pH–conductivity—external magnesium added graph and the phosphate concentration in the water. For each mole of phosphorus removed, the molar ratio of Mg:P was 1.3–2.0 at the transition point. The magnesium concentration in the water matrix was also determined by the hardness test method; this method was found to be suitable for quick, on-site testing.

Modeling and optimization of struvite precipitation process for phosphorus recovery from wastewater

The recovery of phosphorus from wastewater following struvite precipitation pathway can provide a viable and sustainable source for phosphorus. This pathway is important because current phosphorus ore reserves are expected to be exhausted within the next few decades, or, the recovery from the ores will become more costly. However, the recovery of phosphorus from wastewater is not straightforward due to the complexities arising from the number of variables and chemistry involved with the precipitation of phosphorus as struvite. Modeling the dynamic nature of the crystallization phenomenon appears to be the method of choice to control the process. In this study, a dynamic control model for phosphorus recovery process via struvite crystallization was developed. This model incorporated both chemistry and control software, and was used to increase the efficiency and ease of process operation of a pilot-scale fluidized crystallizer. This process model was the basis of an automatic controller that had the capability to manipulate flows and chemical additions, and thereby control the system at a desired set point. The control model was then used as a prediction tool to determine conditions that influence the supersaturation ratio — the primary control parameter — of the process.