F. A. Koch

Controlling factors for simultaneous nitrification and denitrification in a two-stage intermittent aeration process treating domestic sewage

Abstract This bench-scale research investigated the controlling factors for simultaneous nitrification and denitrification (SND) in a 2-stage, intermittent aeration (IA) process, designed for nitrogen and phosphorus removal. The 2-stage process consisted of an anaerobic zone followed by an oxidation–reduction potential (ORP) controlled, intermittently aerated, completely mixed (IACM), tank. The three independent variables examined were the average ORP level, organic substrate (acetate and methanol) dosage and aeration cycle. The sewage used was completely of residential origin. Nitrogen balance clearly indicated that the nitrogen loss, due to SND in the aeration tank, contributed 10% to 50% of the influent TKN to the overall nitrogen removal. Significant differences in both nitrification and denitrification in the IACM tank were observed, when different average ORP levels were applied to the aeration control; this proved that absolute ORP can be used as a real-time control parameter for SND. Under low DO and intermittent aeration conditions, acetate and methanol additions improved nitrification over the entire dosage range and denitrification at relatively low dosages. Finally, a longer aeration cycle, with a zero-DO period, appeared to favor sequential nitrification and denitrification (SQND), not SND.

Phosphorus recovery from wastewater through struvite formation in fluidized bed reactors: a sustainable approach

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.

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.

Production and Basic Morphology of Struvite Crystals from a Pilot-Scale Crystallization Process

A pilot-scale, struvite crystallization process was operated using anaerobic digester supernatants from two, full-scale, treatment plants as influent. It was found that the produced struvite crystals were easily separated from the process and were composed of very pure struvite (91.2 % to 94.1 % purity), with small amounts of calcium and carbonate, and traces of iron and aluminum. Most of the harvested struvite crystals, which were an aggregation of numerous fine crystals, were round, hard and larger than 1.5 mm in mean diameter. The crystal retention time in the reactor and the magnesium dosage in the supernatant appeared to have a significant effect on the crystal size, hardness and morphology.

A survey of prefermenter design, operation and performance in Australia and Canada

We have compiled recent data from nine full-scale prefermenters in Australia and Canada. Using this data, we compare their design, operation and performance. The design parameters of importance are the prefermenter configuration, the fraction of total flow that is fed to the prefermenter, the prefermenter volume and the hydraulic and solids residence time (HRT and SRT). With respect to prefermenter performance, we use the rate of volatile fatty acid (VFA) production to compare prefermenter efficiency. A number of other performance indicators are also used to compare the output of the prefermenters (for example total mass of VFA produced). All side-stream prefermenters compared in this study have relatively similar rates of VFA production (typically 14 to 28 mg/L/h), which indicates that they all perform with similar efficiencies, regardless of their respective type.

Exploring the Determination of Struvite Solubility Product from Analytical Results

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 (Ksp ) determined at 20°C for anaerobic digester supernatant from the Penticton, B.C. Advanced Wastewater Treatment Plant, was found to vary from 8.46 × 10−15 (pKsp =14.07) to 1.3x10−13 (pKsp =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 × 10−15 (pKsp =14.28) to 2.12 × 10−13 (pKsp =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.

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...

Recovery of phosphorus from dairy manure: a pilot-scale study

Phosphorus was recovered from dairy manure via a microwave-enhanced advanced oxidation process (MW/H2O2-AOP) followed by struvite crystallization in a pilot-scale continuous flow operation. Soluble phosphorus in dairy manure increased by over 50% after the MW/H2O2-AOP, and the settleability of suspended solids was greatly improved. More than 50% of clear supernatant was obtained after microwave treatment, and the maximum volume of supernatant was obtained at a hydrogen peroxide dosage of 0.3% and pH 3.5. By adding oxalic acid into the supernatant, about 90% of calcium was removed, while more than 90% of magnesium was retained. As a result, the resulting solution was well suited for struvite crystallization. Nearly 95% of phosphorus in the treated supernatant was removed and recovered as struvite.

Anaerobic Co-Digestion of Combined Sludges from a Bnr Wastewater Treatment Plant

The fate of phosphorus contained in waste activated sludges from a biological nutrient removal plant was investigated in pilot-scale, co-digestion studies at a full-scale wastewater treatment plant. In these studies, co-digestion of primary fermenter and waste activated sludges resulted in a significant release of the biologically-bound sludge phosphorus. As much as 80% of phosphate removed during treatment was released to the supernatant during anaerobic digestion. Phosphate release was found to be independent of digester hydraulic retention time at the values tested (20 vs. 10 day). Co-digestion also impacted other aspects of digester operation, including volatile solids reduction and total gas and methane production. Jar tests, conducted to evaluate the efficiency of various chemical treatment methods for removing phosphate from digester supernatants, revealed that lime, alum and ferric chloride all proved equally effective. Overall, ferric chloride at a dosage of 2 g l−1 was found to be the most effec...

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.