Design and Optimization of Fluidized Bed Reactor Operating Conditions for Struvite Recovery Process from Swine Wastewater

Response surface methodology for process optimization in livestock wastewater treatment: A review

With increasing demand for meat and dairy products, the volume of wastewater generated from the livestock industry has become a significant environmental concern. The treatment of livestock wastewater (LWW) is a challenging process that involves removing nutrients, organic matter, pathogens, and other pollutants from livestock manure and urine. In response to this challenge, researchers have developed and investigated different biological, physical, and chemical treatment technologies that perform better upon optimization. Optimization of LWW handling processes can help improve the efficacy and sustainability of treatment systems as well as minimize environmental impacts and associated costs. Response surface methodology (RSM) as an optimization approach can effectively optimize operational parameters that affect process performance. This review article summarizes the main steps of RSM, recent applications of RSM in LWW treatment, highlights the advantages and limitations of this technique, and provides recommendations for future research and practice, including its cost-effectiveness, accuracy, and ability to improve treatment efficiency.

Effect of recirculation and hydraulic loading rate on ammonium and phosphate recovery from fertilizer industry wastewater

This study aimed to determine the optimum recirculation ratio and hydraulic loading rate for the recovery process of ammonium and phosphate, and study the formation, morphology, and structure of struvite crystals. This study provides a crystallization method to treat fertilizer wastewater using a continuous system and recirculation, including a fluidized bed reactor (FBR). Ammonium and phosphate were recovered from fertilizer industry wastewater using a continuous FBR under different recirculation ratios (3, 6, and 9) and loading rates (0.39 L/min, 0.59 L/min, and 0.79 L/min). MgCl2 was used as the precipitant with a 1.5:1 molarity ratio [Mg2+]:[PO43-]. The results showed that 55.71% phosphate and 49.69% ammonium could be recovered at recirculation ratio and hydraulic loading rate were 9 and 0.39 L/min, respectively. Scanning electron microscopy-energy diffraction X-ray analysis showed that the formed crystals comprised 80% struvite. Further, a high recirculation ratio and low loading rate resulted in higher ammonium and phosphate recovery efficiencies. These results indicated that a long detention time of treated wastewater can increase the nutrient recovery.

Optimization and modeling of ammonia nitrogen removal from anaerobically digested liquid dairy manure using vacuum thermal stripping process

During anaerobic digestion (AD) of liquid dairy manure, organic nitrogen converts to ammonia nitrogen (NH₃-N) and subsequently escalates the NH₃-N concentrations in manure. Among different available NH₃-N removal processes treating anaerobically digested liquid dairy manure (ADLDM), vacuum thermal stripping is reported to be an effective technique. However, none of the studies have performed multi-parameter optimization, which is of utmost significance in maximizing process efficiency. In this study, critical operational parameters for vacuum thermal stripping of NH₃-N from ADLDM were optimized and modeled for the first time via integrating grey relational analysis (GRA)-based Taguchi design, response surface methodology (RSM), and RSM-artificial neural network (ANN). The initial experimental trials conducted using the GRA coupled with Taguchi L₁₆ orthogonal array revealed the order of influence of the process parameters on NH₃-N removal as vacuum pressure (kPa) > temperature (°C) > treatment time (min) > mixing speed (rpm) > pH. The values of the first three most influential operating parameters were then further optimized and modeled using RSM and RSM-ANN models. Under the optimized conditions (temperature: 69.6 °C, vacuum pressure: 43.5 kPa, and treatment time: 87.65 min), the NH₃-N removal efficiency of 93.58 ± 0.59 % was experimentally observed and was in line with the RSM and RSM-ANN models' predicted values. While the RSM-ANN model showed a better prediction potential than did the RSM model when compared statistically. Moreover, the nutrient contents (nitrogen, N and sulfur, S) of the recovered NH₃-N as ammonium sulfate ((NH₄)₂SO₄) were in reasonable agreement with the market-available (NH₄)₂SO₄ fertilizer. The results presented in this study provide important insights into improving the treatment process performance and will help design and operate future pilot- and full-scale vacuum thermal stripping processes in dairy farms.

Effect of acetic acid on struvite precipitation: An exploration of product purity, morphology and reaction kinetics using central composite design

Phosphorus recovery has attracted increasing interest due to the potential depletion of phosphorus resources. One promising solution is to recover phosphorus via struvite precipitation from wastewater or other waste that is in rich of phosphate. However, product quality control during such process is always challenging due to the variation and complexity of wastewater compositions. For example, subcritical wet oxidation (SCWO) effluent is rich in phosphorus and nitrogen but contains a large amount of acetic acid, while its effect on struvite recovery is hardly known. Therefore, central composite design (CCD), considering pH, acetic acid level, Mg level and Ca level, was used to evaluate the effect of acetic acid on struvite purity, phosphorus removal, morphology and reaction kinetics. The experimental data were statistically analysed by analysis of variance (ANOVA) and principal components analysis (PCA). The results indicate that pH and Mg level have a significant impact on phosphorus removal (pH: p-value < 0.0001, Mg: p-value < 0.0001) and struvite purity (pH: p-value = 0.0410, Mg: p-value < 0.0001), Ca level only affects the struvite purity (p-value = 0.0333). The presence of acetic acid, within the studied range (8.77-34.53 mM), has a negligible effect on struvite morphology, phosphorus removal and reaction kinetics, but a slightly positive effect on struvite purity. Findings of this research would be beneficial to determine the feasibility of acetic acid-rich wastewater as a phosphorus source for struvite recovery.

Optimization and Modeling of Ammonia Nitrogen Removal from High Strength Synthetic Wastewater Using Vacuum Thermal Stripping

Waste streams with high ammonia nitrogen (NH3-N) concentrations are very commonly produced due to human intervention and often end up in waterbodies with effluent discharge. The removal of NH3-N from wastewater is therefore of utmost importance to alleviate water quality issues including eutrophication and fouling. In the present study, vacuum thermal stripping of NH3-N from high strength synthetic wastewater was conducted using a rotary evaporator and the process was optimized and modeled using response surface methodology (RSM) and RSM–artificial neural network (ANN) approaches. RSM was first employed to evaluate the process performance using three independent variables, namely pH, temperature (°C) and stripping time (min), and the optimal conditions for NH3-N removal (response) were determined. Later, the obtained data from the designed experiments of RSM were used to train the ANN for predicting the responses. NH3-N removal was found to be 97.84 ± 1.86% under the optimal conditions (pH: 9.6, temperature: 65.5 °C, and stripping time: 59.6 min) and was in good agreement with the values predicted by RSM and RSM–ANN models. A statistical comparison between the models revealed the better predictability of RSM–ANN than that of the RSM. To the best of our knowledge, this is the first attempt comparing the RSM and RSM–ANN in vacuum thermal stripping of NH3-N from wastewater. The findings of this study can therefore be useful in designing and carrying out the vacuum thermal stripping process for efficient removal of NH3-N from wastewater under different operating conditions.

Phosphorous and Silica Recovery from Rice Husk Poultry Litter Ash: A Sustainability Analysis Using a Zero-Waste Approach

Phosphate rocks are a critical resource for the European Union, and alternative sources to assure the future production of a new generation of fertilizers are to be assessed. In this study, a statistical approach, combined with a sustainability evaluation for the recovery of materials from waste containing phosphorus (P), is presented. This work proposes a strategy to recover P and silica (SiO2) from rice husk poultry litter ash (RHPLA). The design of experiment (DoE) method was applied to maximize the P extraction using hydrochloric acid (HCl), with the aim to minimize the contamination that can occur by leachable heavy metals present in RHPLA, such as zinc (Zn). Two independent variables, the molar concentration of the acid, and the liquid-to-solid ratio (L/S) between the acid and RHPLA, were used in the experimental design to optimize the operating parameters. The statistical analysis showed that a HCl concentration of 0.34 mol/L and an L/S ratio of 50 are the best conditions to recover P with low Zn contamination. Concerning the SiO2, its content in RHPLA is too low to consider the proposed recovery process as advantageous. However, based on our analysis, this process should be sustainable to recover SiO2 when its content in the starting materials is more than 80%.

Removal of Aniline and Benzothiazole Wastewaters Using an Efficient MnO2/GAC Catalyst in a Photocatalytic Fluidised Bed Reactor

This work presents an efficient method for treating industrial wastewater containing aniline and benzothiazole, which are refractory to conventional treatments. A combination of heterogeneous photocatalysis operating in a fluidised bed reactor is studied in order to increase mass transfer and reduce reaction times. This process uses a manganese dioxide catalyst supported on granular activated carbon with environmentally friendly characteristics. The manganese dioxide composite is prepared by hydrothermal synthesis on carbon Hydrodarco^® 3000 with different active phase ratios. The support, the metal oxide, and the composite are characterised by performing Brunauer, Emmett, and Teller analysis, transmission electron microscopy, X-ray diffraction analysis, X-ray fluorescence analysis, UV-Vis spectroscopy by diffuse reflectance, and Fourier transform infrared spectroscopy in order to evaluate the influence of the metal oxide on the activated carbon. A composite of MnO₂/GAC (3.78% in phase α-MnO₂) is obtained, with a 9.4% increase in the specific surface of the initial GAC and a 12.79 nm crystal size. The effect of pH and catalyst load is studied. At a pH of 9.0 and a dose of 0.9 g L^-1, a high degradation of aniline and benzothiazole is obtained, with an 81.63% TOC mineralisation in 64.8 min.

Nutrient recovery from swine wastewater at full-scale: An integrated technical, economic and environmental feasibility assessment

In this study, the technical, economic and environmental attributes of a full-scale nutrient recovery process connected to the centralized swine wastewater treatment facility (CSWTF) were evaluated. The performance of the process was assessed by introducing influent to the recovery reactor from different components of the CSWTF such as sedimentation tank (swine wastewater) and biological treatment reactor (biologically oxidized material and supernatant of the biologically oxidized material). The results of technical performance assessment revealed that the O-P recovery (87.1-90.7%) and NH₄-N removal (66.9-72.1%) efficiencies from the influent of biological treatment reactor were significantly higher than the influent from sedimentation tank (81.7 and 19.8%, respectively, p < 0.05). The economic evaluation elucidated that by increasing the treatment capacity of the recovery reactor from 30 m³/d to 100 m³/d, operating expenses could be covered through the commercialization of struvite, while it would take around seven years to get back the capital investment. Additional economic savings could also be possible when using the recovered struvite as a fertilizer raw material along with other environmental benefits. Considering the current farming practices in Korea, the complete recovery of O-P from CSWTFs as struvite could drop the soil phosphorus surplus by 40%, minimize the phosphatic fertilizer consumption by 6.4% and ultimately reduce CO₂ equivalent emissions of 6522 tons/year in comparison to chemical fertilizer production. However, during the continuous operation of the full-scale nutrient recovery process, influent characteristics need to be incessantly monitored and adjusted to the optimum conditions to improve the economics of recovered products. Overall, the nutrient recovery process at full-scale not only solves the problem of treating highly polluted swine wastewater but also helps to ensure societal and environmental sustainability.

Optimizing the Processing Factor and Formulation of Oat-Based Cookie Dough for Enhancement in Stickiness and Moisture Content Using Response Surface Methodology and Superimposition

Despite the utilization of dusting flour and oil to reduce dough stickiness during the production process in food industry, they do not effectively help in eliminating the problem. Stickiness remains the bane of the production of bakery and confectionery products, including cookies. In addition, the high moisture content of cookie dough is unduly important to obtain a high breaking and compression strengths (cookies with high breaking tolerance). This study was conducted in light of insufficient research hitherto undertaken on the utilization of response surface methodology and superimposition to enhance the stickiness and moisture content of quick oat-based cookie dough. The study aims at optimizating, validating and superimposing the best combination of factors, to produce the lowest stickiness and highest moisture content in cookie dough. In addition, the effect of flour content and resting time on the stickiness and moisture content of cookie dough was also investigated, and microstructure analysis conducted. The central composite design (CCD) technique was employed and 39 runs were generated by CCD based on two factors with five levels, which comprised flour content (50, 55, 60, 65, and 70%), resting time (10, 20, 30, 40, and 50 min) and three replications. Results from ANOVA showed that all factors were statistically significant at p < 0.05. Flour content between 56% and 62%, and resting time within 27 and 50 min, resulted in dough with high stickiness. High-region moisture content was observed for flour content between 60% and 70%, and within 10 and 15 min of resting time. The optimized values for flour content (V1) = 67% and resting time (V2) = 10 min. The predicted model (regression coefficient model) was found to be accurate in predicting the optimum value of factors. The experimental validation showed the average relative deviation for stickiness and moisture content was 8.54% and 1.44%, respectively. The superimposition of the contour plots was successfully developed to identify the optimum region for the lowest stickiness and highest moisture content which were at 67–70% flour content and 10–15 min resting time.

Simultaneous Removal of Pollutants and Recovery of Nutrients from High-Strength Swine Wastewater Using a Novel Integrated Treatment Process

Simple Summary

Due to the increasing trend of swine consumption in recent decades, swine husbandry practices have become more intensive in Korea. Intensive swine farming practices inevitably result in an increment of wastewater production. Treatment of high strength swine wastewater (SWW) is therefore becoming a matter of concern in Korea. Moreover, with the increasing number of swine heads, swine farms are having issues with malodor, sanitation, and disease control. In this study, a novel integrated treatment process was tested for the simultaneous removal of pollutants and nutrient recovery from high strength swine wastewater. The integrated treatment process used in this study successfully removed the nutrients and other pollutants through biological treatment, recovered the nutrients using struvite crystallization process and decolorized as well as disinfected the effluent before discharge into water bodies by electrochemical treatment. Therefore, using the proposed integrated treatment process, it might be possible to ensure efficient SWW management along with societal and environmental sustainability.

Abstract

In this study, a novel treatment approach combining biological treatment, struvite crystallization, and electrochemical treatment was developed and its efficiency for the simultaneous removal of pollutants and recovery of nutrients from high strength swine wastewater (SWW) was verified. For all the parameters, maximum removal efficiencies in the lab-scale test were obtained in the range of 93.0–98.7% except for total solids (TS) (79.4%). Farm-scale process showed overall removal efficiencies for total nitrogen (TN), total phosphorus (TP), soluble total organic carbon (sTOC), and color as 94.5%, 67.0%, 96.1%, and 98.9%, respectively, while TS, suspended solids (SS), ammonium nitrogen (NH₄-N), and ortho-phosphate (O-P) concentrations were reduced by 91.5%, 99.6%, 98.6%, and 91.9%, respectively. Moreover, the struvite recovered from SWW showed heavy metal concentrations within the range of the Korean standard for fertilizers and feedstocks and thus, suggesting its potential application as fertilizer and in animal feed production. Using the proposed process, the SWW was converted to liquid compost as a quick-acting fertilizer, struvite as a slow-release fertilizer, and the decolorized and disinfected effluent after electrochemical treatment was safe for discharge according to Korean standard. Therefore, the novel integrated treatment process used in this study can be considered as a solution for SWW management and for the simultaneous removal and recycling of nutrients (N and P).