Raw Sewage Treatment by Coagulation/Flocculation and Ozonization

doi:10.21203/rs.3.rs-4870203/v1

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Raw Sewage Treatment by Coagulation/Flocculation and Ozonization

https://doi.org/10.21203/rs.3.rs-4870203/v1

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Coagulation/flocculation and ozonation are two treatment methods commonly used for effluents. Coagulation/flocculation destabilizes the charged particles in the medium, causing them to aggregate for subsequent separation through decantation or flotation. On the other hand, ozonation is an advanced oxidative treatment that can be employed for effluent polishing. This study aimed to evaluate the effectiveness of combining coagulation/flocculation and ozonation as an alternative treatment for raw sewage collected at the Curupy treatment station in Sinop, MT. The experiments were conducted in batches, involving seven doses of tannin-based coagulant (ranging from 0 to 300 mg L^-1) with and without ozonation (for 40 minutes). Parameters such as pH, color, turbidity, UV absorbance (UV abs), chemical oxygen demand (COD), and biochemical oxygen demand (BOD) were measured before and after the treatments. The results demonstrated that the pH values remained relatively unaffected by the treatments. However, ozonation consistently led to superior removal rates compared to non-ozonation for color, turbidity, UV abs, COD, and BOD (with removal percentages of 86, 87, 74, 71, and 55% respectively, compared to 60%, 74, 49, 58, and 36% without ozonation. For color and turbidity, stabilization of removal rates occurred at coagulant dosages above 100-150 mg L^-1, regardless of ozone contact. Overall, the employed treatments ensured that the sewage met the required conditions for discharge into bodies of water and also made it suitable for potential reuse, thanks to the significant clarification of the effluent. The treatments effectively removed suspended and colloidal solids from the sewage as well as dissolved compounds.

Clarification

Physical-chemical

Polishment

Tertiary treatment

Sewage is primarily composed of water (99.9%) with a minor fraction (0.1%) consisting of solid materials, including organic matter, microorganisms, and chemical substances derived from human feces and urine. Additionally, sewage contains substances such as soaps, detergents, phosphates, sulfates, as well as recalcitrant compounds like hormones and drug residues. Fats and minerals are also present (Kich and Böckel 2017).

Sewage treatment involves a combination of physical (decantation/sedimentation), chemical (coagulation/flocculation), and biological (aerobic and anaerobic microbiota) processes. These treatments are typically carried out in sewage treatment stations (STSs), which replicate the natural purification capacity of watercourses more efficiently in terms of time and space (Pereira et al. 2020).

Coagulation has gained significant acceptance in the treatment of urban and industrial effluents among physical-chemical processes (Pereira et al. 2020). Coagulants have gained popularity over the years due to their effectiveness in removing particulate matter and reducing parameters such as turbidity and solids (Faye et al. 2017; Lima et al. 2020).

Coagulants can be of chemical origin (such as aluminum sulfate, ferric chloride, and ferric sulfate) or natural origin (derived from plants, seeds, etc.) (Lima et al. 2020; Silveira et al. 2020). Natural coagulants, particularly those based on tannins, offer advantages over chemical coagulants in terms of sludge generation and volume reduction (Lima et al. 2020; Silveira et al. 2020). However, the selection of a coagulant depends on factors such as efficiency, sludge reuse, and cost-effectiveness.

Coagulation/flocculation has demonstrated satisfactory results in effluent treatment, contributing to the removal of turbidity, color, UV_254nm absorbance (UV abs.) (Silva et al. 2022), as well as total solids, chemical and biochemical oxygen demands (COD and BOD), nitrogen, and phosphorus (Gao et al. 2021).

Furthermore, a physical-chemical treatment can be combined with other technologies, such as the use of activated carbon as an adsorbent (Bacelo et al. 2020), biological processes (Andrade and Brito 2021), and advanced processes like hydrogen peroxide and ozone (Silveira et al. 2020).

Considering alternative techniques for the degradation of organic matter, particularly those that involve slower or more challenging decomposition processes, the most commonly employed treatments involve the use of high potential oxidizing agents such as advanced oxidative processes (AOPs) and ozone (Pinheiro et al. 2019; Trevizani et al. 2019).

AOPs are characterized by the generation of hydroxyl radicals (•OH), which possess a high oxidation potential and exhibit promising outcomes in the degradation of recalcitrant compounds (Ameta et al. 2019; Silveira et al. 2020; Wu et al. 2021). These radicals are generated through reactions involving ozone, hydrogen peroxide, ultraviolet or visible irradiation, and catalysts (Araújo et al. 2021).

Ozone, with its high reduction power (E0 = 2.08 V) (Araújo et al. 2021; Oliveira et al. 2018), can directly react with molecules or indirectly generate hydroxyl radicals that facilitate the oxidation process (Arimi 2017; Araújo et al. 2021).

The oxidation of both organic and inorganic compounds in the presence of ozone occurs through direct reaction (electrophilic attack) at an acidic pH, targeting specific functional groups (Lajayer et al. 2019). At a basic pH, the reaction proceeds indirectly through hydroxyl radicals, which, due to their lower selectivity, react with organic compounds up to 109 times faster than oxidants like hydrogen peroxide (H₂O₂) (Arimi 2017; Ghernaout and Elboughdiri 2020).

The application of ozone as an oxidant has yielded positive outcomes, particularly in terms of color and UV absorption removal (Hoffmann et al. 2020), organic material degradation (COD and BOD) (Gomes and Schoenell 2018), and turbidity reduction (Schons et al. 2018).

Ozone is typically generated through the corona effect, which involves the passage of atmospheric air (or oxygen) between two electrodes with a significant potential difference, resulting in a high electrical discharge (approximately 10 kV). This discharge causes the dissociation of O₂ molecules, leading to the formation of atomic oxygen, which subsequently reacts with another O₂ molecule to produce ozone (Scandelai et al. 2021).

In this context, the present study aims to assess the efficiency of the coagulation/flocculation + ozonation process in treating raw sewage, focusing on the removal of suspended and dissolved elements measured through parameters such as apparent color, turbidity, UV abs, and chemical and biochemical oxygen demands.

The test samples were obtained from the Curupy sewage treatment plant located in Sinop, MT. The treatment system of the plant had a capacity to process 0.06 m³ s^− 1 of sewage and comprised upflow anaerobic reactors (UASB) followed by an activated sludge system.

Sewage was collected at the desander outlet (raw sewage) and stored in polyethylene containers. After collection, the effluent was taken to the laboratory and stored under refrigeration. The experiments were carried out at the Water and Waste Laboratory (WWL), at the Federal University of Mato Grosso, Sinop Campus.

The effluent was initially characterized by determining its pH, color, turbidity, ultraviolet absorbance at 254 nm (UV abs), chemical oxygen demand (COD), and biochemical oxygen demand (BOD). Apparent color, turbidity, and UV abs values were measured using a colorimeter, turbidimeter, and spectrophotometer, respectively. BOD was determined using the incubation method at 20°C for 5 days, while COD was measured using the hot acid digestion method with dichromate (Table 1).

Table 1

Parameters and analysis methods applied for the initial characterization of sewage
Analyzed parameter	Unit	Method
pH	-	Potentiometric
apparent color	mg Pt-Co L^− 1	Photocolorimetric
turbidity	NTU	Nephelometric
Abs UV	cm^− 1	Spectrophotometric
COD	mg L^− 1	Hot acid digestion with potassium dichromate
BOD	mg L^− 1	Incubation for 5 days at 20°C without seed

The characteristics of the sewage (Table 2) reveal that it possesses an optimal pH for biological treatment, although it exhibits a high apparent color value, suggesting the presence of solids. The BOD and COD values indicate a moderate level of organic material. These findings emphasize the necessity for sewage treatment prior to its discharge into water bodies.

Table 2

Average characteristics of sewage used in treatment.
Parameters	Initial values
pH	7.18
Apparent color (mg Pt Co L ^− 1 )	1930.00
Turbidity (NTU)	177.33
UV abs (cm ^− 1 )	1.72
COD (mg L ^− 1 )	655.56
BOD (mg L ^− 1 )	200.89

In coagulation/flocculation processes, the pH values play a crucial role in destabilizing particle loads and influencing the removal of pollutants (Kamiwada et al. 2020). However, since the initial pH value of the raw sewage falls within the ideal range for the action of the coagulant, no adjustments to the pH were made.

Regarding ozonation, the degradation of compounds primarily occurs through direct oxidation at an acidic pH. However, at neutral pH, there is an increase in the decomposition of ozone into hydroxyl radicals (OH), leading to enhanced degradation of compounds through indirect oxidation. Therefore, in the ozonation process, removal efficiencies are influenced by both direct reactions (with greater selectivity but less power) and indirect reactions (with lower selectivity but greater power) due to the sample's pH being close to neutral (Ghernaout and Elboughdiri 2020). Thus, both ozone (O₃) and the hydroxyl radical (OH) contribute to the removal mechanisms.

The experimental process was divided into two stages (Fig. 1), namely primary treatment and effluent polishing.

2.1. Step 1 – Primary Treatment: Coagulation/Flocculation

Following the initial characterization, the effluent was subjected to the jar test, where various dosages of coagulant were added. Upon completion of the primary treatment, including coagulation, flocculation, and sedimentation, samples were collected for further characterization. A portion of the sample was then used for the subsequent ozonation test (Fig. 1).

Table 3 outlines the conditions employed during the primary treatment, including the rotational speeds and their corresponding durations.

Table 3

Steps and programming for testing in *jar test*
Stage	Rotation (rpm)	Time (min)
Coagulation – fast step	120	2.5
Flocculation – slow step	20	20
Decantation	0	20

2.2. Step 2 - Effluent Polishing through Ozonation

Ozone gas was employed for the sewage polishing step. The ozone generator utilized atmospheric air and operated based on the corona effect generation mechanism. Its nominal production capacity was 0.4 g O³ per hour.

To conduct the experimental tests, the iodometric method, as adapted from APHA (2017) and Almeida Junior (2006), was employed.

Portions (0.2 L) of effluent were introduced into the reactor. In the ozone capture cylinders, 0.2 L of potassium iodide (KI), with a concentration of 20 g L^− 1, were added. The reactor and the test tubes were covered, and the tests were started at the pre-defined ozonation time.

The KI contents were removed from the test tubes and transferred to Erlenmeyers for the quantification of excess ozone (non-reacted), using the iodometric method. This procedure was performed with distilled water for blank tests.

The quantification of residual ozone, mass flow, was determined using the following:

$$\:{O}_{3res}\left({mg\:min}^{-1}\right)=\frac{V*N*24}{t}$$

Where:

V is the volume of sodium thiosulphate used in the potassium iodide titration (mL);

N is the normality of sodium thiosulphate (0.1 N);

t is the previously determined exposure time (min);

24 is the conversion factor (24000 mEq L per 1000 mL L).

The consumed ozone was determined by the difference in the values of gas not consumed by the water (white-B) and by the effluent (Ef) (2).

$$\:{O}_{3co}{(mg\:min}^{-1})=\:{O}_{3res}\left(B\right)-{O}_{3res}\left(Ef\right)$$

Where:

O_3co is consumed ozone (mg min^− 1);

O_3res(B) is the residual ozone in the blank (mg min^− 1);

O_3res(Ef) is the residual ozone in the effluent test (mg min^− 1).

The experimental design was completely randomized (DIC), in a 7x2 factorial scheme, with 7 concentrations of coagulant (0, 50, 100, 150, 200, 250 and 300 mg L-1) and 2 times of contact with ozone (0 and 40 min), totaling 14 treatments, in triplicate.

The results were submitted to analysis of variance (ANOVA), and when statistical difference was detected (p ≤ 0.05), mean and regression tests were used.

3.1. Effect of Treatments

The analysis of variance revealed significant differences (p ≤ 0.05) for color, turbidity, and COD concerning the sources of variation: coagulant dosages and ozonation time. Additionally, significant differences (p ≤ 0.05) were observed for UV abs and BOD, specifically in relation to the source of variation, ozonation time. However, the interaction between the sources of variation did not yield any significant difference (Table 4).

The pH value remained unchanged across all treatments, with a slight increase of approximately 11% at the end of the experiments compared to the initial values. Previous studies have shown that tannins do not affect the pH of the effluent as they do not deplete the alkalinity of the medium. Moreover, tannins exhibit a broad range of action within the pH scale, from 4.5 to 8.0 (Silveira et al. 2021).

Table 4

Summary of the analysis of variance for the evaluated parameters
Factors	pH	Color	Turbidity	UV	COD	BOD
Dosage (Dose)	0.8563	0.0000	0.0000	0.0600	0.0280	0.2401
Ozonation time (OT)	0.1598	0.0000	0.0001	0.0001	0.0019	0.0013
Dose X OT	0.4653	0.2902	0.6353	0.6817	0.7744	0.8247

Values less than or equal to 0.0500 classify the treatments as significant at the 5% probability level.

For the UV abs parameter, a remarkable removal of 74% was observed when the sewage underwent ozone treatment. This increase in removal was significantly higher compared to the coagulation treatment alone (Table 5).

Studies by Lima and Abreu (2018) have indicated that the presence of humic and inorganic substances absorbs ultraviolet light. Additionally, Mena et al. (2020); Munyasamy et al. (2020) have observed that UV absorbance indicates the presence of aromatic and unsaturated substances (chromophores). Hence, the removal of UV abs demonstrates the ozone treatment's effectiveness in decomposing aromatic and unsaturated molecules.

Since color and UV abs are closely related to the presence of chromophoric substances in the liquid phase (Ghalebizade and Ayati 2016), any modifications in chromophoric compounds can cause noticeable interference in both the visible (color) (Table 6) and ultraviolet (abs) ranges (Table 5).

Regarding BOD, the coagulant treatment resulted in a removal of 36% (Table 5). Conversely, the utilization of ozone led to a significant increase in BOD removal, with an average value of 55%. While the achieved removal levels may not be as high as those for parameters such as color and turbidity, ozonation proves to be efficient in reducing the organic load in effluents, preparing them for further treatment. Furthermore, it can be inferred that ozone facilitates the degradation of organic matter, mineralizing more complex molecules and breaking them down into simpler forms that still contribute to BOD. Thus, ozone acts upon the effluent without generating substantial BOD removal.

Schons et al. (2018) obtained superior results (86%) in BOD removal compared to the findings presented in this study. The authors employed ozone in treating a combined raw landfill leachate and domestic sewage, with an ozonation time close to 30 hours and an ozone concentration approximately six times greater than that utilized in our research.

Table 5

Abs UV and BOD removal as a function of ozonation time, %
OT (min)	UV abs.	BOD
0	49	36
40	74	55

In terms of apparent color, the utilization of ozonation resulted in an impressive removal rate of 86% (Table 6). This significant efficiency in removing colloidal and suspended materials clearly demonstrates the effectiveness of ozonation. Moreover, visual observations during the ozonation process revealed noticeable changes in the effluent's color, transitioning from gray to white/transparent (Fig. 2). This color transformation aligns with previous findings reported by Silva et al. (2016).

Additionally, Muniyasamy et al. (2020) propose that the reduction in color is linked to O³ attacking the chromophoric carbon double bonds, resulting in the formation of "bleached" molecules like aliphatic acids and aldehydes, which are generally more biodegradable. This ozone-induced breakdown of double bonds generates simpler molecules, aligning with the BOD results obtained.

Furthermore, ozone exhibits potential for bleaching effluents, particularly in situations where reuse is a consideration.

Analyzing the removal of color in relation to the coagulant dosage (Fig. 3a), a certain level of stability in removal efficiency (~ 80%) is observed when the dosage exceeds 75 mg/L. However, for coagulant dosages greater than 50 mg/L, removal rates above 70% were achieved.

The outcomes for color removal align with the findings of Jawad et al. (2017); Silveira et al. (2021) when treating domestic sewage and surface water, respectively. These studies demonstrate the coagulant's remarkable efficiency in removing particulate matter and further underscore the potential of combining ozone with coagulation/flocculation processes.

Table 6

Removal of color, turbidity and BOD as a function of ozonation time, %
OT (min)	Color	Turbidity	COD
0	60	74	58
40	86	87	71

In terms of turbidity, an average removal of 87% was achieved when the effluent came into contact with ozone (Table 6). However, even without the application of ozone gas, significant removal was observed. This can be attributed to the coagulant's ability to eliminate suspended solids.

The turbidity removal values obtained in this study were higher than those reported by Camilo et al. (2019) when assessing the removal of physical attributes from sewage through ozonation.

The reduction in turbidity when effluents are exposed to ozone is attributed to the ability of ozone to break down particles and organic compounds with greater mass, converting them into dissolved molecules (Miklos et al. 2018).

Regarding the range of coagulant dosages used for turbidity removal (Fig. 3b), it was noted that a certain stabilization of removal occurred for dosages exceeding 150 mg/L. Oliveira (2016) achieved similar results using tannin in the dosage range of 200 to 250 mg/L at pH 7. Silveira et al. (2020) evaluated tannin coagulant at varying concentrations ranging from 261 mg/L to 1568 mg/L. Their experimental tests showed that the best results were obtained with a natural pH (without pH adjustment), achieving 100% turbidity removal in sanitary effluents. For this experiment, good removals were also observed in the dosage range of 50 mg/L.

Both natural and artificial coagulants consist of large molecular chains with positive or negative charges, allowing them to adsorb particles in their vicinity (Zhao et al. 2019). Tannin-based coagulants are widely used for turbidity removal due to their ability to neutralize surface charges of suspended colloids, aiding in agglomeration and sedimentation (Silveira et al. 2021).

The behavior of COD removal was similar to that of color and turbidity parameters, with a removal rate of 71% when the effluent was exposed to the oxidizing gas (Table 6). The primary treatment targeted the removal of particulate and colloidal COD, while ozonation primarily affected the dissolved COD portion.

Hoffmann et al. (2020), studying the effect of ozonation in raw landfill leachate treatment, reported good COD removal at pH 7, a value very similar to the average found in this study (7.18).

Lei and Li (2014), when applying ozone in sewage, suggested that a portion of the COD removal may be attributed to the stripping (mass exchange between liquid and gas) of organic gases. In other words, the chemical oxygen demand may have varied due to both ozone oxidation and mass transfer between the liquid (effluent) and gaseous (ozone) phases.

COD was also influenced by coagulant dosages (Fig. 3c), although it did not follow the same stabilization trend observed for color and turbidity. Dosages ranging from 50 to approximately 160 mg/L exhibited better removal rates (70% or more), while at other concentrations, removal rates above 50% were observed.

The COD removal results obtained in this study were slightly higher than those reported by Silveira et al. (2020) when evaluating the potential application of physicochemical processes using tannin coagulant and advanced oxidative ozonation in the treatment of sanitary effluents. In their study, the authors achieved 48% COD removal at the optimal tannin concentration of 523 mg/L. Coagulants generate a larger volume of sludge compared to other treatment technologies, resulting in a higher concentration of organic matter in the generated sludge and effectively removing significant amounts of waste from the effluent (Ghalebizade and Ayati, 2016; Kamiwada et al. 2020).

With the BOD and COD data, it was possible to estimate the biodegradability (Fig. 4) as a function of the primary treatment and the combination of primary and ozone.

The results demonstrated variations in the BOD/COD ratio depending on the treatment employed. Coagulant dosages exceeding 250 mg/L for CF and 175 mg/L for CF + O³ fell below the optimal range indicative of good biodegradability (> 0.5) (Scandelai et al. 2021). Nevertheless, the treatments still led to an improvement in the effluent's biodegradability compared to the raw effluent, which had a BOD/COD ratio of 0.30.

3.2. Consumed Ozone

The consumed ozone values exhibited a tendency to increase with higher coagulant dosages (Fig. 5). It appears that the addition of the coagulant promotes ozone consumption without proportionally enhancing the removal efficiency of the evaluated parameters (Fig. 3).

A plausible explanation for this behavior is that the ozone may react with the residual coagulant from the coagulation process. This hypothesis is supported by the drastic clarification observed in the effluent after ozonation. Ozone has the ability to react with a wide range of functional groups, leading to the breakdown of carbon-carbon double bonds and the formation of lower molecular weight by-products (Fonseca et al. 2017; Ikehata and Li, 2018; BELÉ et al. 2021).

3.3. Residual Values

The applied treatment demonstrated high removal values for the analyzed parameters, particularly for color and COD. However, it is worth noting that turbidity and BOD are of greater significance, as they indicate the ability of the CF + O³ combination to meet regulatory standards for discharge (Table 7).

The residual values of the evaluated parameters were generally lower for the ozone treatment, with the exception of pH. By combining coagulation (dosages above 200 mg/L) with ozone (40 minutes of treatment time), the effluent acquires characteristics suitable for release into water bodies, as demonstrated by BOD removal rates exceeding 60%.

Table 7

Residual values obtained for the analyzed parameters of raw and treated effluents as a function of contact with ozone and doses of coagulant
Parameters	0 minutes of _O3		40 minutes of _O3
Parameters	Eph. gross	Eph. Treated	Eph. gross	Eph. Treated
0 mg L^− 1
pH ⁽¹⁾	7.2	7.6 ^*	7.2	8.2 ^*
Color (mg Pt Co L ^− 1 ) ⁽²⁾	1930.0	1698.3	1930.0	744.0
Turbidity (NTU) ⁽³⁾	177.3	104.6	177.3	65.1 ^*
UV abs. 254nm (cm ^− 1 )	1.7	1.2	1.7	0.7
COD (mg L ^− 1 )	655.6	337.2	655.6	291.7
BOD (mg L ^− 1 ) ⁽⁴⁾	200.9	156.9	200.9	138.2
50 mg L^− 1
pH	7.2	7.7 ^*	7.2	8.1 ^*
Color (mg Pt Co L ^− 1 )	1930.0	808.33	1930.0	265.3
Turbidity (NTU)	177.3	60.9 ^*	177.3	28.2 ^*
UV abs. 254nm (cm ^− 1 )	1.7	0.6	1.7	0.3
COD (mg L ^− 1 )	655.6	196.7	655.6	162.8
BOD (mg L ^− 1 )	200.9	110.2	200.9	94.7
100 mg L^− 1
pH	7.2	8.0 ^*	7.2	8.1 ^*
Color (mg Pt Co L ^− 1 )	1930.0	760.3	1930.0	221.0
Turbidity (NTU)	177.3	55.3 ^*	177.3	19.2 ^*
UV abs. 254nm (cm ^− 1 )	1.7	0.6	1.7	0.3
COD (mg L ^− 1 )	655.6	235.6	655.6	137.8
BOD (mg L ^− 1 )	200.9	124.6	200.9	95.9
150 mg L^− 1
pH	7.2	8.0 ^*	7.2	8.0 ^*
Color (mg Pt Co L ^− 1 )	1930.0	643.3	1930.0	166.3
Turbidity (NTU)	177.3	33.3 ^*	177.3	8.1 ^*
UV abs. 254nm (cm ^− 1 )	1.7	0.6	1.7	0.4
COD (mg L ^− 1 )	655.6	227.8	655.6	131.1
BOD (mg L ^− 1 )	200.9	114.6	200.9	81.8
200 mg L^− 1
pH	7.2	8.1 ^*	7.2	8.0 ^*
Color (mg Pt Co L ^− 1 )	1930.0	478.0	1930.0	182.3
Turbidity (NTU)	177.3	24.7 ^*	177.3	7.9 ^*
UV abs. 254nm (cm ^− 1 )	1.7	0.8	1.7	0.4
COD (mg L ^− 1 )	655.6	237.8	655.6	148.3
BOD (mg L ^− 1 )	200.9	131.2	200.9	65.1 ^*
250 mg L^− 1
pH	7.2	8.0 ^*	7.2	8.0 ^*
Color (mg Pt Co L ^− 1 )	1930.0	626.0	1930.0	156.7
Turbidity (NTU)	177.3	22.7 ^*	177.3	12.0 ^*
UV abs. 254nm (cm ^− 1 )	1.7	0.8	1.7	0.5
COD (mg L ^− 1 )	655.6	376.7	655.6	173.3
BOD (mg L ^− 1 )	200.9	141.2	200.9	79.7 ^*
300 mg L^− 1
pH	7.2	7.9 ^*	7.2	7.9 ^*
Color (mg Pt Co L ^− 1 )	1930.0	501.3	1930.0	174.7
Turbidity (NTU)	177.3	24.0 ^*	177.3	13.9 ^*
UV abs. 254nm (cm ^− 1 )	1.7	1.2	1.7	0.5
COD (mg L ^− 1 )	655.6	271.1	655.6	175.0
BOD (mg L ^− 1 )	200.9	123.8	200.9	65.7 ^*

Caption. Ideal ranges according to CONAMA resolutions 357/2005 and 430/2011 for disposal in class 2 rivers [(1) – (5–9); (2) – (75 mg Pt Co L ^-1 ); (3) – (100 NTU); (4) – (minimum removal of 60%)]. For UV abs. and COD there are no minimum values. Residuals marked with asterisks (*) highlight values where release standards were achieved after treatment.

Several studies have been conducted on the integration of ozone with other advanced oxidation processes (AOPs) and its combination with conventional treatments for polishing purposes (Ikehata and Li 2018; Hidayaturrahman and Lee 2019; Silveira et al. 2020; Sun et al. 2019; Li et al. 2022). The efficiency of biological treatments has been shown to increase when combined with the coagulation/flocculation + ozone + biological treatment sequence (Mella et al. 2018; Scandelai et al. 2021). Additionally, high BOD removals have been achieved by Silva and Daniel (2015) when using ozone followed by chlorine disinfection. Pastore et al. (2018) compared different treatments for landfill leachate and found that the most effective approach was the combination of biological treatment and ozonation, when considering the RBGSB (batch sequential granular biofilter) reactor along with other treatments such as hydrogen peroxide, ultraviolet and hydrogen peroxide, and ozonation.

The results presented in this study, along with findings from other researchers, highlight the significant potential of ozonation in effluent treatment.

The combination of coagulation/flocculation and ozonation proves to be highly efficient in treating sanitary sewage effluents. Coagulation/flocculation and coagulation/flocculation + ozonation demonstrated remarkable removal rates for apparent color (> 80%), turbidity (~ 87%), and COD (> 71%). However, the highest removal rates for UV abs. (74%) and BOD (55%) were achieved only when ozonation was applied.

AUTHOR CONTRIBUTIONS

Conceptualization: Matheus Caneles Batista Jorge, Milene Carvalho Bongiovani Roveri and Roselene Maria Schneider; Methodology: Matheus Caneles Batista Jorge, Milene Carvalho Bongiovani Roveri and Roselene Maria Schneider; Formal analysis and investigation: Matheus Caneles Batista Jorge, Milene Carvalho Bongiovani Roveri, Roselene Maria Schneider and Adriana Garcia do Amaral; Writing - original draft preparation: Matheus Caneles Batista Jorge; Writing - review and editing Matheus Caneles Batista Jorge, Milene Carvalho Bongiovani Roveri, Roselene Maria Schneider and Karoline Carvalho Dornelas; Supervision: Milene Carvalho Bongiovani Roveri, Roselene Maria Schneider, Adriana Garcia do Amaral and Karoline Carvalho Dornelas.

ACKNOWLEDGEMENTS

The authors would like to thank the Institute of Agricultural and Environmental Sciences, Federal University of Mato Grosso (UFMT-Sinop), for the financial support.

Declaration of interests

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

-Ethical Approval: Not applicable.

-Consent to Participate: Not applicable.

-Consent to Publish: Not applicable.

-Funding: No funding was received to assist with the preparation of this manuscript.

-Competing Interests: All authors certify that they have no affiliations with or involvement in any organization or entity with any financial interest or non-financial interest in the subject matter or materials discussed in this manuscript.

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Raw Sewage Treatment by Coagulation/Flocculation and Ozonization

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Abstract

Figures

1. INTRODUCTION

2. MATERIAL AND METHODS

2.1. Step 1 – Primary Treatment: Coagulation/Flocculation

2.2. Step 2 - Effluent Polishing through Ozonation

24 is the conversion factor (24000 mEq L per 1000 mL L).

3. RESULTS AND DISCUSSION

3.1. Effect of Treatments

3.2. Consumed Ozone

3.3. Residual Values

4. CONCLUSIONS

Declarations

References

Supplementary Files

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