Application of a new type of Si–Al porous clay material as a solid phase support for immobilizing Acidovorax sp. PM3 to treat domestic sewage

Abstract

A novel Si–Al porous clay material W (reprocessed from ceramic waste) was used for Acidovorax sp. strain PM3 immobilization to promote the growth of strains and improve nitrogen and phosphorus removal performance in water treatment systems. The porous clay material W was characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscopy indicating that porous clay material W was a type of mullite with 63.52 m²/g specific surface area. After immobilization, the maximum biomass increased 2.7 times the specific growth rate and the removal rates of chemical oxygen demand (COD), ammonia (NH₄⁺–N), and total phosphorus (TP) by the immobilized PM3 were 42.99, 29.19, and 11.76% higher than the free strain after 24 h. The Monod equation showed that the growth rate and processing speed of immobilized PM3 increased. The maximum adsorption capacities of COD and NH₄⁺–N onto porous clay material W were 2.33 and 0.32 mg/g on the basis of Langmuir isotherm. The removal capacities of COD, NH₄⁺–N, and TP by the immobilized PM3 were 588.24, 20.37, and 5.06 mg/l, respectively, as shown by kinetic studies. These results demonstrated that porous clay material W could improve the efficiency of microbial nitrogen and phosphorus removal, and the immobilized microorganism system could effectively treat domestic sewage. The adsorption isotherms can well describe the adsorption process. The maximum adsorption capacity of COD and NH₄⁺–N on porous clay material W is 2.33 and 0.32 mg/g, respectively. Kinetic studies showed that the removal capacity of immobilized PM3 to COD, NH₄⁺–N, and TP was 58.824, 20.37, and 5.06 mg/l, respectively.

Keywords

Si–Al porous clay material immobilization microorganism kinetics domestic sewage Acidovorax sp.PM3

Introduction

Carbon, nitrogen, and phosphorus are the major pollutants in China’s domestic sewage. Some conventional treatment methods such as sequencing batch reactor (Sarti et al., 2007), simultaneous partial nitrification, anammox denitrification (Ding et al., 2018), constructed wetland (Lutterbeck et al., 2018), and membrane bio-reactor (Bach et al., 2018) have limitations in removing carbon, nitrogen, and phosphorus from sewage. Therefore, high-efficiency, low-cost, and environmental-friendly tools are urgently needed.

Microorganism immobilization technologies have been widely used for the treatment of domestic sewage in rural areas and other fields of pollution control such as insecticides, surfactants, textile dyes, heavy metal, volatile organic pollutants, and PAH (Bergero and Lucchesi, 2018; Biswas et al., 2015; Dong et al., 2017; Geed et al., 2018; Kiran et al., 2018; Sarioglu et al., 2017). This technology confines free microorganisms by physical or chemical means. This leads to high-density materials with high biological activities. These materials must be used repeatedly with easy control of biological concentration, fast reaction speed, low loss of microorganisms, easy separation of products, and miniaturized treatment equipment (Eroglu et al., 2012; Li and Li, 2013). In recent years, research on this technology has become very active and has rapidly developed. There are many types of carrier materials used for immobilization such as zeolite, polyvinyl alcohol–sodium alginate–calcium nitrate, sodium alginate, and polyurethane foams (Chen, 2009; Dong et al., 2014; Gan et al., 2019; Nie et al., 2010). Compared with natural carriers and polymer materials, inorganic carriers are characterized by good stability, low toxicity to microorganisms, resistance to microorganisms, low cost, and long life.

In particular, porous clay mineral materials have good properties as the inorganic carrier and have unique advantages such as good mechanical strength and high porosity. The pore structure and large specific surface area provide more surface area to anchor bacterial species. The unique lamellar structure of clay mineral materials leads to special properties such as adsorption, plasticity, and ion exchange (Gołub and Piekutin, 2018; Pentyala et al., 2018; Xu et al., 2018). Various porous clay materials have been used to treat sewage including attapulgite, magnetic porous ceramsite, bentonite, clay mineral Fe(II)-montmorillonite, novel clay ceramic particles (Cheng et al., 2014; Han et al., 2019, 2013; Vinuth et al., 2015; Xu et al., 2019). Although using porous clay materials to treat sewage is very useful and effective, some of the widely utilized materials are expensive. The mechanism of the changes in the microenvironment—which affect the surface of the complex and its adsorption—is an important research content of microbial immobilization (Zhou et al., 2018). Analysis methods commonly used to describe the immobilization removal mechanism include the Monod equation, adsorption kinetics, and adsorption isotherms (Alshameri et al., 2018; Fatimah, 2018; Singh and Pandey, 2016).

In this study, a cheap and effective novel porous clay material called Si–Al porous clay material W (PCMW) was used to immobilize bacterial PM3. The PCMW before and after adsorption was characterized by X-ray diffraction, X-ray fluorescence, Fourier-transform infrared spectroscopy, and scanning electron microscopy (SEM). To investigate the effect and mechanism of removing carbon, nitrogen and phosphorus in domestic sewage by immobilized strain, adsorption isotherms, Monod equation, and adsorption kinetics were used. As PCMW is a ceramic waste, it not only provides a low-cost sewage treatment technology but also plays a role in waste utilization.

Materials and methods

Preparation of microorganism and simulated domestic sewage for adsorption

PM3 is a Gram-negative aerobic or facultatively anaerobic bacteria with high efficiency for removing nitrogen and phosphorus. It was isolated in 2017 from a soil sample from a stable and high-performing underground filtration system; it had a removal rate of 84.88, 76.00, and 26.85% against COD, NH₄⁺–N, and TP, respectively, in simulated domestic sewage after 48 h. Phylogenetic analysis based on 16S rRNA gene sequences showed that the strain belonged to the genus Acidovorax (trivalent arsenic-oxidized bacteria).

The artificially simulated domestic sewage mainly contains CH₃COONa, (NH₄)₂SO₄, KH₂PO₄, CaCl₂, and MgSO₄; the concentrations of COD, NH₄⁺–N, and TP are 300, 15, and 7 mg/l, respectively.

Preparation and characteristics of the immobilizing support PCMW

The PCMW adopted here is the Si–Al ceramic porous material. It has pore sizes of 30–1000 µm and a porosity of 30–90%. This porous material was synthesized from two natural clays: CN-01 and CN-02. CN-01 and CN-02 were from Changning Yunnan. The contents of muscovite were 28.1 and 16.9 wt%, quartz was 15.4 and 10.4 wt%, potash feldspar was 1.3 and 0.6 wt%, and kaolinite was 55.2 and 72.1 wt%. The CN-01 and CN-02 were uniformly mixed in a mixing machine at a mass ratio of 2:7. Water was then added to obtain a uniform mixture. The mixture was aged at room temperature. After drying, it was placed in an electric furnace for firing (800°C with an oxidizing environment for 8 h). It was then naturally cooled to room temperature to obtain a silica–alumina porous clay material.

A digital photomicrograph of PCMW is shown in Figure 1. This was obtained from a portable digital microscope Dino-lite (a product from Anpeng Technology Co., Ltd). A polycrystalline X-ray diffractometer (XRD; X’Pert Pro, Panalytical B.V., The Netherlands) was adopted for PCMW, and the results demonstrate that PCMW was a type of mullite (Figure AM1). The XRF (Nicolet 380FT-IR, Thermo Electron Corporation) showed qualitative analysis on PCMW, which suggested that the main chemical components of PCMW are SiO₂, Al₂O₃, K₂O, Fe₂O₃, and impurities. Their contents are 56.78, 37.11, 2.78, 1.58, and 1.75 wt%, respectively.

Figure 1.

Photograph of PCMW.

Activation of PM3 and its immobilization to simulate domestic sewage treatment

The preserved PM3 was inoculated in liquid beef extract peptone medium and activated for 24 h. Here, 10 ml of the bacterial solution was placed in a centrifuge tube and centrifuged for 10 min at 10,000 r/min to remove the supernatant. This led to a pure sample. The value of OD600 was regulated to 1 with sterilized water in an aseptic processing desk; 5 ml of the bacterial solution was inoculated into 200 ml of the simulated sewage. This was sterilized with a pipette gun and 2 g of PCMW was added to each Erlenmeyer flask. The bacterial solution was cultivated on a shaking table at 30°C and 150 r/min. The concentrations of OD600, COD, NH₄⁺–N, and TP in the simulated sewage were measured at 0, 4, 8, 12, 24, 36, 48, 72, 96, and 120 h. All tests were done in triplicate.

Adsorption experiments

Two grams of PCMW and 200 ml simulated sewage with single pollutants were added to each Erlenmeyer flask. The initial concentrations of COD in the simulated sewage were 50, 100, 200, 300, and 400 mg/l; the initial concentrations of NH₄⁺–N were 10, 20, 30, 40, and 50 mg/l; the initial concentrations of TP were 2, 4, 6, 8, and 10 mg/l. The concentrations of COD, NH₄⁺–N, and TP in the simulated sewage were measured after 8 h. All tests were done in triplicate.

Isotherm modeling

Adsorption mechanisms are extremely complicated. Therefore, no simple theory can adequately explain adsorption characteristics. Several isotherm models have been used to describe the relationship between an adsorbate and an adsorbent. The Langmuir and Freundlich isothermal adsorption equations are the most widely used isothermal adsorption equations (Kim et al., 2011). The main output of the adsorption isotherm study describes the equilibrium correlation between the concentration of adsorbate on the adsorbent and in solution as well as the distribution at adsorbent interfaces (Kausar et al., 2018). The Langmuir and Freundlich expressions are shown in equations (1) and (2), respectively

Q_{e} = \frac{Q_{m} K_{L} C_{e}}{1 + K_{L} C_{e}}

(1)

Q_{e} = K_{F} C_{e}^{1 / n}

(2)

Here, Q_e is the equilibrium adsorption (mg/g), Q_m is monolayer adsorption (mg/g), K_L is the Langmuir constant at a certain temperature, C_e is the concentration of the pollutant residual in the water as an adsorption equilibrium is reached (mg/l), and K_F and n are empirical constants.

Kinetic modeling

A study of dynamics helped explain the degradation mechanism of the free and immobilized PM3 in simulated wastewater. In the case of single-substrate limited process, the Monod equation is often used as follows

μ = μ_{\max} \frac{S}{K_{s} + S}

(3)

Here, μ is the growth rate of microorganisms (time⁻¹), μ_max is the maximum specific growth rate of microorganisms in saturated concentration (time⁻¹), K_s is the saturation constant and is also known as the half rate constant (mg/l), and S is the substrate concentration of organic matter (mg/l).

However, this equation can be varied in different cases. Based on equation (3), previous studies showed that the modified Monod model was suitable for a substrate with a mixture of organic wastewater (Okpokwasili and Nweke, 2005; Sun et al., 2011). For the removal of organic matter from wastewater, the Monod equation above can be rewritten into equation (4). After integrating both sides of equation (4), a linear expression of the Monod equation is shown in equation (5)

- \frac{d s}{d t} = \frac{V_{\max}}{K_{s} + S}

(4)

\frac{1}{S_{0} - S} l n \frac{S_{0}}{S} = \frac{V_{\max}}{K_{s}} \frac{X_{t}}{S_{0} - S} - \frac{1}{K_{s}}

(5)

Here, S₀ is the initial concentration of the matrix in the simulated wastewater (mg/l), S is the concentration of the matrix at a certain period of time (mg/l), V_max is the maximum ratio of microbial growth in saturated concentration (h⁻¹), K_s is the saturation constant (mg/l), and X_t is the gross biomass inside the system. The linear relationship can be found between $\frac{1}{S_{0} - S} l n \frac{S_{0}}{S}$ and $\frac{X_{t}}{S_{0} - S}$ by taking $\frac{1}{S_{0} - S} l n \frac{S_{0}}{S}$ as the ordinate and $\frac{X_{t}}{S_{0} - S}$ as the abscissa. This straight line has a slope expressed as $\frac{V_{\max}}{K_{s}}$ and an intercept on the abscissa expressed as $- \frac{1}{K_{s}},$ where K_s and V_max can be determined using a graphical method.

The removal of pollutants via the immobilized PM3 is a complex process. The pseudo-second-order kinetic relationship assumes that chemisorption is dominant and controls the adsorption as a rate-limiting step (Hamza et al., 2018). The pseudo-second-order kinetics could not reliably determine the removal kinetics of pollutants, and the pseudo-first-order kinetics and modified pseudo-first-order kinetics were adopted to understand the possible mechanism associated with the adsorption of pollutants onto PCMW. This offers insight into enhancing the efficiency of the adsorption process (Negm et al., 2018). The pseudo-first-order kinetic equation is expressed as equation (6)

Q_{t} = Q_{e} (1 - \exp (- K_{1} t))

(6)

Terms Q _e and Q _t are the degradation amount as equilibrium is reached and at the moment of t, respectively (mg/l). Term K₁ is a pseudo-first-order removal rate constant (h⁻¹). Here, time is the abscissa and ln(q_e − q_t) is the ordinate. Thus, a pseudo-first-order kinetic linear fitting was plotted for the removal of COD, NH₄⁺–N, and TP in the simulated sewage using PCMW and the immobilized PM3.

Analysis

Index of simulated domestic sewage

The key indexes COD, NH₄⁺–N, TP, and OD600 were measured by fast digestion spectrophotometry, Nessler’s reagent spectrophotometry, and Mo–Sb anti-spectrophotometry and spectrophotometry, respectively.

SEM

The SEM was used to observe the external cell morphology. The culture solution was centrifuged at 8000 r/min for 3–5 min, and then 2.5% glutaraldehyde was added after discarding the supernatant. Fresh glutaraldehyde was used to fix for 2–4 h. The cells were washed with PBS and then dehydrated with gradient ethanol at 15 min each: 30, 50, 70, 85, and 95%; 100% ethanol was used twice. Isoamyl acetate was then used for a final wash at 20 min per round with two rounds of treatment. The cells were added to a glass slide and dried naturally in a dust-free environment; they were then sputter coated before imaging with a Quanta 200 FEG SEM (FEI Instruments, USA).

XRD and Fourier transform infrared spectroscopy (FT-IR)

Powder X-ray diffraction (XRD) experiments were performed between 2° and 70° (2θ) with a step size of 0.02° using ZSXPrimus II (Rigaku Corporation, Japan) and identified using JCPDS files. FT-IR was performed between 400 and 4000 cm⁻¹ with a Nicolet FTIR-iS10 (Thermo Fisher Scientific, USA) using the KBr pellet technique.

Results and discussion

SEM analysis before and after strain immobilization

The SEM was used to study the PCMW and immobilized PM3 (Figure 2). The results showed the structure of PCMW, the morphology of PM3, and how the PM3 strain clung and grew on the surface and inside of PCMW.

Figure 2.

SEM scan for samples: (a) PCMW, (b) free PM3, and (c) PM3 + PCMW.

The PCMW had a rough surface and pore structure with obvious porous sizes. The specific surface area (S_BET) of PCMW was 63.52 m²/g, the total pore volume was 0.25 cm³/g, and average pore size was 4.06 nm. Thus, the PM3 more easily clung to the sample. The PM3 cells are bacilliform. The PM3 clung and grew on the surface of PCMW and inside its pore structure after being immobilized. PCMW with bigger pores had more surface area and more space for microorganism to move and grow. Bigger pores also had better mass transfer, which led to better oxygen and nutrient transport. The oxygen and nutrients were decomposed and utilized by the microorganisms. Metabolites produced by the microorganism were discharged from the PCMW at a faster speed; this facilitated microorganism growth. The SEM data showed that PCMW promoted the growth of PM3.

Removal rate of free PM3 with immobilized PM3

Figure 3 shows the growth curves of PCMW as well as free and immobilized PM3. The immobilized PM3 entered the logarithmic phase in advance beginning at 8 h and ending at 48 h; however, the free PM3 began at 36 h and ended at 72 h. The immobilized PM3 had a longer logarithmic growth period than free PM3. Compared with the free strain, the maximum biomass of the immobilized PM3 increased by 19.71%, which is more than 2.7-fold the specific growth rate of the free PM3. This is consistent with the literature (Gabelish et al., 2006; Lee et al., 2012).

Figure 3.

Growth curves of PCMW, as well as free and immobilized PM3 (T: 30°C; shaking: 150 r/min). PCMW: porous clay material W.

PM3 with the same concentration was inoculated in the simulated domestic sewage under the same conditions. The immobilized strain nicely removes carbon, nitrogen, and phosphorus from the simulated domestic sewage compared with the free strain. In 24 h, the removal rates of the free PM3 against COD, NH₄⁺–N, and TP were 24.71, 16.41, and 6.87%, respectively; the removal rates of the immobilized PM3 against COD, NH₄⁺–N, and TP were 67.70, 45.60, and 18.63%, respectively. This is an increase of 42.99, 29.19, and 11.76%, respectively, compared with the free strain (Figure 4). At 120 h, the removal rates of the immobilized PM3 against pollutants COD, NH₄⁺–N, and TP were 99.99, 91.36, and 55.98%, respectively. This is 5.11, 12.36, and 19.13% higher than the free PM3.

Figure 4.

Removal in wastewater by PCMW, free and immobilized PM3: (a) effect of COD, (b) effect of NH₄⁺–N, and (c) effect of TP (T: 30°C; shaking: 150 r/min). PCMW: porous clay material W.

Throughout the process, the increased removal rates of COD, NH₄⁺–N, and TP in the immobilized PM3 were higher than the free strain. This implies that there is synergistic behavior between PM3 and PCMW. The immobilized PM3 showed the best removal behavior. Immobilized PM3 predisposed the pollutant before the free PM3 and improved the removal rate. This was likely because immobilization contributes to the growth of the strain, so more carbon, nitrogen, and phosphorus could be utilized (Li et al., 2017). The PCMW could also adsorb carbon and nitrogen.

Isothermal adsorption curve of PCMW against pollutants

The changes in concentrations of COD, NH₄⁺–N, and TP were determined after adsorption for 8 h. The adsorption quantity of PCMW against the pollutants was then calculated. The Langmuir and Freundlich model simulations were performed using C_e as the abscissa and Q_e as the ordinate (Figure 5). The adsorption constants of the Langmuir and Freundlich adsorption models were obtained using the linear regression method, and the fitting parameters of the two isotherm equations are shown in Table 1.

Figure 5.

Langmuir and Freundlich isotherm adsorption of PCMW: (a) COD, (b) NH₄⁺–N, and (c) TP (T: 25°C, pH: 7).

Table 1.

Related parameters of Langmuir and Freundlich isotherms.

Isotherm type	Parameters	Adsorbate
Isotherm type	Parameters	COD (mg/g)	NH₄⁺–N (mg/g)	TP (mg/g)
Langmuir	Q_m	2.3333	0.3243	–
	K_L	0.0478	0.0095	–
	R ²	0.5567	0.9234	–
Freundlich	K_F	4.4771	0.4418	0.0031
	n	2.7762	1.4065	0.2347
	R ²	0.9716	0.9679	0.7125

COD: chemical oxygen demand; TP: total phosphorus.

The values of R² were regarded as a measure of the goodness of fit of the experimental data for the isotherm models. Table 1 shows that TP could not simulate the Langmuir isotherm adsorption. The R² of the Freundlich isotherm adsorption was 0.71 and n < 1 indicating that it was not valid for the adsorption of TP on PCMW. The R² of COD and NH₄⁺–N with the Freundlich isotherm were higher than the Langmuir isotherm (0.95); thus, these species were fitted with the Freundlich model. This is due to the variance in the adsorption sites on PCMW; the adsorption occurred on non-homogeneous adsorptive sites but with a higher surface coverage (Hamza et al., 2018; Xu et al., 2018). The Freundlich theory stated that K_F could be used as the basis for evaluating adsorption capacity—PCMW had a strong adsorption capacity for COD; n > 1 for preferential adsorption, and the larger value of n indicated that the adsorbate was more likely to be adsorbed by the adsorbent. The COD and NH₄⁺–N were easily absorbed by PCMW with n of 2.78 and 1.41.

The Langmuir isotherm data in Table 1 show that the adsorption saturation capacities of PCMW against COD and NH₄⁺–N were 2.33 and 0.32 mg/g at 50 mg/l and 25°C and pH 7. This is lower than other porous material adsorbents for NH₄⁺–N in the literature: wood biochar, 0.06–1.33 mg/g (Tian et al., 2016); natural Chinese clinoptilolite, 0.40–0.95 mg/g (Wang et al., 2006); and Posidonia oceanica fibers, 1.73 mg/g (Salah et al., 2011).

Degradation kinetics of free and immobilized PM3 against pollutants

Figure AM2 describes the degradation kinetics of free and immobilized PM3 on COD, NH₄⁺–N, and TP in simulated wastewater via the Monod model. The Monod equation and related parameters are shown in Table 2.

Table 2.

Degradation kinetics of free and immobilized PM3 via the Monod equation and related parameters.

Adsorbent	Adsorbate	Related parameters
Adsorbent	Adsorbate	K_s (mg/l)	V_max (h⁻¹)	R ²
Free strain PM3	COD	454.5455	54.3636	0.9681
	NH₄⁺–N	19.9601	0.8363	0.9518
	TP	4.8544	0.0213	0.9187
Immobilized strain PM3	COD	588.2353	75.4118	0.9085
	NH₄⁺–N	20.3666	0.8635	0.9734
	TP	5.0582	0.0334	0.9521

COD: chemical oxygen demand; TP: total phosphorus.

The Monod equation could nicely simulate the removal of all the pollutants especially NH₄⁺–N in the simulated sewage using free and immobilized PM3. The degradation kinetic simulation results are shown in Figure AM2, and the determination coefficient R² (all the pollutants: >0.9, NH₄⁺–N: >0.95) in Table 2. Given the slope and intercept of the equation, the K_s and V_max of the free and immobilized PM3 degrades COD to 454.55 mg/l, 54.361 h⁻¹ and 588.24 mg/l, 75.41 h⁻¹; NH₄⁺–N was 19.96 mg/l, 0.84 h⁻¹ and 20.37 mg/l, 0.86 h⁻¹; TP was 4.85 mg/l, 0.02 h⁻¹ and 5.06 mg/l, 0.03 h⁻¹. For all pollutants, the immobilized PM3 increased both the K_s and V_max relative to the free PM3, which implies that PM3 increased its growth rate, processing speed, and processing capacity after immobilization. This corresponds to the growth curves and removal results above.

FT-IR analysis before and after immobilization

The FT-IR spectra before and after the immobilization are presented in Figure 6. Absorption peaks at 3313.00 and 3128.41 cm⁻¹ were the contraction of O–H, while the absorption peaks at 1635.15 and 1618.15 cm⁻¹ were the bending of O–H. This might be caused by the sewage being adsorbed into PCMW leading to the overlap of hydroxyl groups from the absorption of water (Yujia L, Danyang Y, Luz S, et al., 2018). The bands at 1400.48–897.32 and 555.49–464.94 cm⁻¹ correspond to stretching bands of Si–O (Alshameri et al., 2018). Peaks related to hydrogen bonding of water were at 3416.00 cm⁻¹ with water bending at 1618.15 and 1635.15 cm⁻¹ (Erdoğan and Erdoğan, 2011). There was only one additional absorption peak at 2357.69 cm⁻¹ before immobilization. This is the stretching vibrational frequency of C–O (Li T, Song F, Zhang J, et al., 2020). In comparison, the immobilization mainly affected the drift of the peak resulting in a new peak indicating that the interaction between microorganisms and PCMW was mainly physical. The additional peak of C–O confirmed immobilization.

Figure 6.

FT-IR spectra before and after immobilization. PCMW: porous clay material W.

Removal kinetics of PCMW and immobilized PM3 against pollutants

The parameters for the pseudo-first-order kinetic equation were calculated on the basis of the nonlinear fitting results (Table 3 and Figure AM3).

Table 3.

Pseudo-first-order kinetic fitting parameters.

Adsorbent	Adsorbate	Related parameters
Adsorbent	Adsorbate	q_e(exp) (mg/l)	q_e(cal) (mg/l)	k₁ (h⁻¹)	R ²
PCMW	COD	31.2692	30.3820	0.0870	0.9272
	NH₄⁺–N	3.3665	3.5857	0.0322	0.9683
	TP	0.1163	0.1166	0.0280	0.9834
Immobilized strain PM3	COD	310.3121	347.6978	0.0350	0.9167
	NH₄⁺–N	16.3464	18.6953	0.0239	0.9778
	TP	2.2620	2.7804	0.0187	0.9522

COD: chemical oxygen demand; PCMW: porous clay material W; TP: total phosphorus.

Besides the removal of COD by PM3, the pseudo-first-order kinetic equation could accurately describe the removal kinetics of the pollutants on PCMW and the immobilized PM3. The R² for all the pollutants were both greater than 0.9 whether the process used PCMW or immobilized PM3. The q_e(exp) and q_e(cal) were also basically the same indicating that the adsorption kinetics of all the pollutants on PCMW and the immobilized PM3 were suitable for pseudo-first-order kinetics model. Except for the adsorption of COD onto PCMW, the calculated value q_e(cal) for all pollutants increased with either PCMW or the immobilized PM3. For PCMW against COD, q_e(exp) was 31.27 mg/l and q_e(cal) for pseudo-first-order kinetics model was 30.38 mg/l. This is different from the 23.33 mg/l for the monolayer adsorption concentration of Langmuir isotherm adsorption. For PCMW and the immobilized PM3, the q_e(cal) of NH₄⁺–N was higher than q_e(exp) (3.37 mg/l). Here, 3.24 mg/l was used for the monolayer adsorption concentration of Langmuir isotherm adsorption; this concentration was closer to q_e(exp). The results indicated that the physical adsorption and the degradation rate for immobilized PM3 were only related to the surface area and pore size of PCMW (Hyun et al., 2018; Yujia L, Danyang Y, Luz S, et al., 2018; Mahdis and Binaeian, 2018). Compared with the removal rate constants k₁, immobilized PM3 were lower for COD, NH₄⁺–N, and TP, but there was less processing capacity due to the time of growth and fixation of the strain. Diffusion was an important factor limiting the first-order rate constant. The results indicated that the adsorption process for pollutants on PCMW was affected by the diffusion resistance of the liquid film; the fitting intercept of the straight line was larger, and the liquid film diffusion was not the only rate-influencing factor (Wan et al., 2018).

Processing capacity of PCMW, free PM3, and immobilized PM3

Table 4 shows the fitting parameters of processing capacity of PCMW, the free PM3, and the immobilized PM3. The processing capacities of the immobilized PM3 were higher than those of the free PM3. The amount of increase for COD, NH₄⁺–N, and TP were 133.69, 11.79, and 0.2038 mg/l. These were higher than adsorption capacities of PCMW for COD (31.27 mg/l), NH₄⁺–N (3.37 mg/l), and TP (0.12 mg/l). This means that the high removal of pollutants by the immobilized PM3 was not only due to the separate action of PCMW and the free PM3 but also due to the increased processing capacity of the PM3 by immobilization, which agreed with other studies (Lou et al., 2019).

Table 4.

Fitting parameters of processing capacity of W, free PM3, and immobilized PM3.

Adsorbent	Isotherm type on which parameters are based	Adsorbate
Adsorbent	Isotherm type on which parameters are based	COD (mg/l)	NH₄⁺–N (mg/l)	TP (mg/l)
PCMW	Langmuir and kinetics	30.3820	3.5857	0.1166
Free strain PM3	Monod	454.5455	19.9601	4.8544
Immobilized strain PM3	Monod and kinetics	588.2353	20.3666	5.0582

COD: chemical oxygen demand; PCMW: porous clay material W; TP: total phosphorus.

PCMW has a positive charge, and the surface of the PM3 is negative (the isoelectric point of the PM3 was 5.5, and the pH of the wastewater was 6.7). Thus, the two were easily combined. This made the PM3 adhere to PCMW. Moreover, many chemical/functional groups of extracellular polymeric substances could be attracted to PCMW, and thus, the PM3 could be immobilized more effectively to promote the ability of the immobilized PM3 to remove pollutants. PCMW is a new type of Si–Al porous material. It offers a place for the free PM3 to adhere, and the pores facilitated the entry of oxygen and nutrients to facilitate the growth of the free PM3. The silicon/aluminum and counter-ions improved the survival and activity of the free PM3 immobilized onto them (Bautista-Toledo et al., 2015; Kiran, MG, Pakshirajan K, and Das G, 2018).

Conclusion

The immobilized PM3 had a remarkable improvement in growth rate and biomass versus free PM3. The immobilized PM3 removed COD, NH₄⁺–N, and TP better than free PM3 via the adsorption effect of PCMW, the biological degradation effects of PM3, and the promoting effect of PCMW to PM3. The removal rates of the immobilized PM3 against COD, NH₄⁺–N, and TP were 99.99, 91.36, and 55.98%, respectively. The interaction of PCMW on pollutants and PM3 was physical. The adsorption capacities of PCMW against COD and NH₄⁺–N were 21.36–30.38 and 3.24–3.59 mg/l with weak adsorption capacity for TP. The degradation capacities of the free PM3 against COD, NH₄⁺–N, and TP were 454.55, 19.96, and 4.85 mg/l. The immobilized PM3 acted against COD, NH₄⁺–N, and TP from 336.37 to 588.24 mg/l, 18.69 to 20.37 mg/l, and 2.75 to 5.06 mg/l, respectively.

Supplemental Material

ADT887819 Supplemental Material - Supplemental material for Application of a new type of Si–Al porous clay material as a solid phase support for immobilizing Acidovorax sp. PM3 to treat domestic sewage

Supplemental material, ADT887819 Supplemental Material for Application of a new type of Si–Al porous clay material as a solid phase support for immobilizing Acidovorax sp. PM3 to treat domestic sewage by Binhui Jiang, Yu Li, Haiyan Wang, Liping Jia, Fei Huang and Xiaomin Hu in Adsorption Science & Technology

Footnotes

Acknowledgments

We thank LetPub () for its linguistic assistance during the preparation of this manuscript.

Declaration of Conflicting Interests

The author(s) disclosed receipt of the following financial support for the research, authorship and/or publication of this article: The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study was financially supported by the Major Project of National Science and Technology (MPNST, 2013ZX07202-010–05) and the National Natural Science Foundation of China (51278090).

ORCID iD

Binhui Jiang

Supplemental Material

Supplemental material is available online for this article.

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