Optimization of a dual-chamber electrolytic reactor with a magnesium anode and characterization of struvite produced from synthetic wastewater.

Diminishing phosphorus resources worldwide requires developing new technologies to recover phosphorus (P) from wastewaters. A lab-scale electrolytic reactor with a magnesium anode was investigated to remove NH4+ and PO43- from synthetic wastewater by producing struvite. The effects of mixing speed, pH, and applied current on struvite yield, NH4+, and PO43- removal efficiencies were first evaluated using a factorial design. Then, the two most significant parameters were further optimized using Central Composite Design (CCD) coupled with Response Surface Methodology (RSM). The struvite was characterized by SEM, XRD, and FT-IR. A 5.7-fold increase in struvite yield was achieved by increasing the applied current from 0.1 to 0.5 A. The three regression equations generated by the CCD/RSM design with applied current and mixing speed as the two independent parameters were highly correlated with the response variables (struvite yield, NH4+ and PO43- removal efficiencies). The desirability analysis showed the best operating condition: current, 0.5 A and mixing speed, 414 rpm, for the reactor system, under which the optimal struvite yield and NH4+ and PO43- removal efficiencies were 4.75 g/L, 93.0%, and 58.4%, respectively. The SEM, XRD, and FT-IR analyses confirmed the high purity and quality of the struvite produced by the electrolytic reactor system.

Microalgae Cultivation Using Screened Liquid Dairy Manure Applying Different Folds of Dilution: Nutrient Reduction Analysis with Emphasis on Phosphorus Removal.

A number of dairies in southern Idaho employed stationary inclined screens to separate large solid particles out of liquid dairy manure. In this way, the total solid content of the liquid dairy manure can drop about 20%. Solids in dairy wastewater cause high turbidities, which could block the incident light, a key factor in the microalgae cultivation process using wastewaters as culture media. In this study, screened liquid dairy manure was used as the microalgae Chlorella vulgaris culture media. The aim was to optimize the dilution folds for the best growth of Chlorella vulgaris and nutrients' reduction with a special focus on phosphorus removal and recovery. Four folds of dilution, designated as 5*, 10*, 15*, 20*, were applied to the liquid dairy manure to alleviate hindrance of the high turbidity together with the high ammonium. Microalgal cultivation removed a significant amount of turbidity and major nutrients. For differently diluted liquid dairy manures, although the initial turbidities varied a lot, the final removal rates were not significantly different, falling in the range of 88.11-91.73%. Chemical oxygen demand (COD) in the 5-fold diluted liquid dairy manure dropped from 6700 to 1200 mg/L, corresponding to a removal rate of 79.81%. For the 10-fold, 15-fold, and 20-fold diluted manures, Chlorella removed around 67-69% of the initial CODs. Total Kjeldahl nitrogen (TKN) was removed at rates ranging from 70.84 to 73.99% from the four differently diluted liquid dairy manures without significant differences. NH4-N was removed most efficiently by 88.92% from the 20-fold diluted liquid dairy manure, and the least at 68.65% from the 5-fold diluted one. Although the original total phosphorus (TP) concentrations were distinctive for each group, the TP removal rates stayed in the range of 52.16 to 65.22%. Scanning electron microscopy (SEM) and energy-dispersive spectrometry (EDS) analysis of the precipitates harvested from the microalgal cultivation suggested possible phosphate precipitate forms. The chelation of Ca or Mg cations by dissolved organic matter (DOM) under alkaline conditions caused by microalgae cultivation could explain the unsatisfactory phosphorus removals observed in this study.

Non-airtight Fermentation of Dairy Manure with Waste Potato Peels and Subsequent Phosphorus Recovery via Struvite Precipitation.

Two-phase anaerobic co-digestion of lignocellulosic crop residues with animal wastes can efficiently generate more biogas compared with the digestion of animal waste alone. Non-airtight fermentation of the mixed substrates is the primary step to hydrolyze complex organics and achieve simultaneous phosphorus release. Recycling phosphorus from tremendous animal wastes is remarkably meaningful regarding non-renewable resource recovery. In this study, the feasibility of a two-step process combining non-airtight fermentation of potato peels with dairy manure and the following struvite precipitation was explored. The hydrolysis and acidification process of the 6-day non-airtight mesophilic fermentation lowered pH to 6.4 under the highest mixed solid content of 4.8%; meanwhile, the ratio of reactive phosphorus to total phosphorus increased from 49.6 to 93.7% accordingly. Struvite formation was successfully induced by adjusting pH to 8.0 and 9.5. Under these two pHs, the precipitates were dominated by struvite as characterized by X-ray diffraction (XRD). Scanning electron microscopy and energy-dispersive spectrometry (SEM-EDS) results indicated that there should exist both struvite and calcium phosphate in the precipitates obtained under the two pHs. pH 8.0 precipitate should contain around 75% struvite, while the proportion rose to about 90% for pH 9.5 precipitate, based on the calculation of respective Mg/P and Ca/P molar ratios.

Nutrient Reduction of Dairy Manure Through Solid-Liquid Separation with Flocculation and Subsequent Microalgal Treatment.

High concentrations of dairy operations in Southern Idaho have brought up big challenges for proper manure management to alleviate the eutrophication stress. In order to explore more technologies confronting the high nutrient load in dairy manure, a sequential process combining enhanced solid-liquid separation through flocculation-centrifuge and the subsequent microalgal growth in the liquid part was studied in this study. Solid-liquid separation by flocculation-centrifuge process, using a natural flocculant chitosan and a flocculation aid kaolin, was optimized through response surface methodology (RSM) technique using central composite design (CCD) method. Under the optimal flocculation-centrifuge pretreatment, i.e., the maximal total suspended solid (turbidity) removal group, turbidity, COD, TKN, and TP have been removed by 92.7%, 72.6%, 58.7%, and 43.0%, respectively. Applying 2-fold dilution, the supernatant from this treatment was further used for microalgae Chlorella vulgaris cultivation. COD, TKN, and TP were further reduced by 82.2%, 90.1%, and 83.4%, respectively. Turbidity was largely removed from the original dairy manure, providing a relatively clear solution that became suitable for photo-mixotrophic culture of microalgae.

Non-airtight fermentation of sugar beet pulp with anaerobically digested dairy manure to provide acid-rich hydrolysate for mixotrophic microalgae cultivation.

Non-airtight fermentation of lignocellulosic agricultural residues with animal wastes is an emerging pretreatment method to produce acid-rich substrates in two-phase anaerobic digestion. Acid-rich hydrolysate could be an excellent feedstock for cultivating microalgae, therefore, the feasibility of a two-step process combining non-airtight fermentation of sugar beet pulp with anaerobically digested dairy manure and mixotrophic microalgae species Chlorella cultivation in the hydrolysate was explored in this study. The hydrolysis and acidification process of 8-day non-airtight fermentation produced up to 8.1 g/L volatile fatty acids under mesophilic condition. Microalgal growths in diluted hydrolysates were compared with that in diluted digested dairy manure (DDM) as a control using experimental data and fitted logistic models. Chlorella grown in the 10-fold diluted DDM showed an exponential decay, while Chlorella cultured in the 3-fold diluted hydrolysate demonstrated the best performance in terms of biomass density, which reached 2.17 g/L within a short period of time.

Pre-digestion to enhance volatile fatty acids (VFAs) concentration as a carbon source for denitrification in treatment of liquid swine manure.

Insufficient denitrification in biological treatment is often a result of the lack of a carbon source. In this study, use of the volatile fatty acids (VFAs) generated via pre-digestion as a carbon source to improve denitrification in sequencing batch reactor (SBR) treatment of liquid swine manure was investigated. The pre-digestion of swine manure was realized by storing the manure in a sealed container in room temperature and samples were taken periodically from the container to determine the VFA levels. The results showed that after 14 days of pre-digestion, the VFA level in the digested liquid was increased by 200%. A polynomial relationship for the VFA level in the digested manure with the digestion time was observed with a correlation coefficient being 0.9748. Two identical SBRs were built and operated on 8-h cycles in parallel, with one fed with pre-digested and the other raw swine manure. There were five phases included in each cycle, i.e., anaerobic (90 min), anoxic (150 min), anoxic/anaerobic (90 min), anoxic/aerobic (120 min), and settle/decant (30 min), and the feeding was split to 600 mL/200 mL and performed at the beginning of and 240 min into the cycle. The SBR fed on pre-digested swine manure achieved successful denitrification with only 0.35 mg/L nitrate left in the effluent, compared to 15.9 mg/L found in the effluent of the other SBR. Nitrite was not detected in the effluent from both SBRs. The results also indicated that there was no negative impact of feeding SBRs with the pre-digested liquid swine manure for treatment on the removal of other constituents such as total solids (TS), volatile solids (VS), suspended solids (SS), volatile suspended solids (VSS), and soluble chemical oxygen demand (COD). Therefore, anaerobic digestion as a pretreatment can be an effective way to condition liquid swine manure for SBR treatment to achieve sufficient nitrate removal.

Study on the effect of total dissolved solids (TDS) on the performance of an SBR for COD and nutrients removal.

In this study, the effect of total dissolved solids (TDS) on the performance of a sequencing batch reactor (SBR) system to treat synthetic wastewater with microbial inoculum was evaluated. The SBR was operated continuously for eight days on a 6-h cycle with anaerobic/anoxic/aerobic phases in each cycle after entering the steady state, and the influent TDS was tested at five levels, i.e., 750, 1500, 3000, 4500, and 6000 mg L-1. The results showed that only two TDS levels (750 and 1500 mg L-1) could achieve good COD removal efficiencies (94.8 and 92.2%, respectively). For TDS levels equal to, or greater than, 3000 mg L-1, a 20% reduction in COD removal efficiency resulted. Different from COD, removal of NH4+-N appeared not to be affected by the TDS content, and a removal efficiency of higher than 97% was obtained, regardless of the TDS content. However, only the lowest two TDS levels achieved high phosphate removals (>99%), and the removal efficiency dropped to 57.8 and 45.9%, respectively, for TDS levels of 3000 and 4500 mg L-1. More interestingly, a phosphate release, instead of uptake, was observed at the TDS level of 6000 mg L-1. It may be concluded that for effective phosphate removal, the TDS level in the liquid should be controlled under 1500 mg L-1, and higher liquid TDS levels were detrimental to the aerobes and could disrupt the aerobic metabolism, leading to the failure of the SBR treatment system. A tendency that raising TDS content would adversely affect the aerobic oxygen uptake rate was observed, which could also result in SBR upset. A power regression with an R of 0.9844 was established between the influent TDS concentration and the TDS removal efficiency, which may be used to estimate the SBR performance in TDS removal based on the influent TDS content.

Feeding schemes and C/N ratio of a laboratory-scale step-fed sequencing batch reactor for liquid swine manure treatment.

This study was undertaken to investigate the effect of two split feeding schemes (600 mL/200 mL and 400 mL/400 mL, designated as FS1 and FS2, respectively) on the performance of a step-fed sequencing batch reactor (SBR) in treating liquid swine manure for nutrient removal. The SBR was run on an 8-h cycle with a repeated pattern of anaerobic/anoxic/aerobic phases in each cycle and the two feedings always occurred at the beginning of each anaerobic phase. A low-level aeration was used (1.0 L/m3.sec) for the anoxic/aerobic phase to facilitate nitrification and phosphorus uptake while reducing the energy consumption. The results showed that FS1 reduced NH4+-N by 98.7% and FS2 by 98.3%. FS1 had 12.3 mg/L NO3-N left in the effluent, while FS2 had 4.51 mg/L. For soluble phosphorus removal, FS1 achieved 95.2%, while FS2 reached only 68.5%. Both feeding schemes achieved ≥ 95% removal of COD. A good power regression was observed between total nitrogen (sum of all three nitrogen species) and the carbon to nitrogen (C/N) ratio, with the correlation coefficients of 0.9729 and 0.9542 for FS1 and FS2, respectively, based on which it was concluded that higher C/N ratios were required to achieve higher nitrogen removal efficiencies.