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Effectiveness of GAC and Ozonated Biofilter to Remove some CECs from WWTP effluents: A review
Wastewater treatment plants deals with treating numerous contaminants based on their capacity. But majorities of contaminants of emerging concern (CECs) remains untreated, which are the world concerned issues now a day. Biodegradation of these contaminants are challenging and interesting by low cost treatment technologies. Biofilter is one kind of low cost technology, where microorganisms could help to break down the complex and large compounds. This paper reviews with some of the significant CECs of different conventional treatment pants effluents which has further been treated with biofilter and hybrid technology like Ozonated-biofilter. The Ozone which is a very effective compound to break complex contaminants, that helps to lead effective removal by biofilter. Some of the contaminants couldn’t show satisfactory result by biofilter, this is because of the structure of that compound that may be unable to break down by Ozone. After all, the removal by ozone-biofilter showed a low cost and effective medium to achieve significant efficiency during treating the effluents. Further research needs to explore based on quantity of contaminants removal and economic perspective.
Keywords: CECs, Ozone, hybrid technology, biofilter
Emerging Contaminants (ECs) are comparatively huge and nearly unregulated by any laws  that are deadly to the human body and as well as to marine life . These deleterious agents mostly detected in landfills, municipal sewage, pharmaceutical production plants, daily household products, wastewater, hospitals, and natural aquatic environment . Variable concentrations may cause hindrance with endocrine system of high organisms, microbiological resistance, and accumulation in soil, plants, and animals , conventional wastewater treatment processes are not able to remove completely of these ECs . ECs include mostly pharmaceutical organic contaminants, personal care products (PCPs), endocrine disrupting compounds (EDCs), surfactants, pesticides, flame retardants, and industrial additives among others. Biologically based WW treatment systems may have the ability of natural ecosystems to reduce pollution from water, cost-effective and workable alternative to conventional WWTPs . Removal technologies can be physical (sorption, photodegradation, volatilization, and sedimentation), chemical (degradation and hydrolysis), and biological (biodegradation and phytoremediation), where biodegradation, phytoremediation, sorption, and photodegradation are the most significant . So, some of ECs may remove certain percentage by WWTP with conventional way.
Pharmaceutical and PCPs include lipid regulators, analgesics, antibiotics, non-steroid anti-inflammatory drugs (NSAIDs), drugs, antiseptics, beta blockers, cosmetics, sun screen agents, food extras, fragrances and and transformation products. Drinking water supplies, ecosystem, and human health can be affected by these kind of products . The occurrence of ECs in the marine environment have been accumulated with many adverse effects, including short-term and long-term toxicity, endocrine disrupting effects and antibiotic resistance of microorganisms . EDCs are exogenous substances or mixtures that change the functions of the endocrine systems and consequently cause adverse health effect in an integral organism, or its progeny . In recent days, there has no specific discharge guidelines and standards for most micropollutants. However, some countries have certain regulation for some specific ECs. Biodegradation of ECs based on some factors which are availability of nutrients, oxygen concentration, pH value, concentration, and bioavailability of contaminants, physical and chemical characteristics of the biomass .
Thus, the aim of this review paper is to evaluate the efficiency of biological and hybrid treatment to remove Emerging Contaminants from wastewater. More comprehensively, the article provided a summary of effectiveness of different conventional wastewater treatment processes for ECs removal and the validation of advanced micro-organismic (GAC Biofilter) treatment process and hybrid treatment i.e. ozonated-microorganism treatment to remove ECs. Moreover, it will discuss about the challenges of biological treatment processes.
- Emerging Contaminants (ECs) in WWTP
2.1 ECs scenario in different countries WWTP
Several review papers studied with the generation of ECs in different water bodies such as influent and effluent from WWTPs ; ; . Several peer-reviewed papers study has showed that raw influent of WWTPs has the concentration of analgesics and non-steroidal anti-inflammatory drugs (NSAID) are ranging from 1.60 ng. L-1 to 373 mg. L-1 in the . The very common compounds were ibuprofen (IBP), DCF, naproxen (NPX), ketoprofen (KPF) and acetaminophen (ACE). For antibiotics, concentrations was found in raw influent to municipal WWTPs between 1.0 ng.L-1 and 32 mg.L-1, and the most commonly researched compounds were sulfamethoxazole, trimethoprim , and ciprofloxacin . In Table 1, it shows several countries WWTPs has the remaining ECs concentration. The concentrations of ECs in influent and effluent of WWTP based on several factors, they are the rate of production, specific sales and practices, metabolism (excretion rate), water consumption per person and per day, the size of WWTPs, environmental persistence and elimination efficacy of wastewater treatment processes .
Table 1: Different ECs in WWTP from different sites and their effective removal efficiency
|Compounds||Sites/Country||Influent in WWTP (μg/L)||Effluent in WWTP (μg/L)||Removal Efficiency (%)||References|
|Diclofenac||EU, Greece, Korea, Sweden, Switzerland, UK, Western Balkan Region||<0.001–94.2||<0.001–0.69||50-85||, , , , , , , , |
|Ibuprofen||China, EU-wide, Greece, Korea, Sweden, UK,
US, Western Balkan Region, Canada
|<0.004–603||ND–55||72–100||, , , , , , , , |
|Naproxen||Greece, Korea, Spain, Sweden, UK, Western Balkan Region, Canada||<0.002–52.9||<0.002–5.09||43.3–98.6||, , , , , , , , |
|Caffeine||China, EU-wide, Greek, Korea, Spain, UK||0.22–209||ND–43.50||49.9–99.6||, , , , , , |
|Triclosan||Spain, UK, US, Greece, Korea, France,
|0.03–23.9||0.01–6.88||71.3–99.2||, , , , , ,
, , , 
|Estrone||China, France, Germany, Italy, Korea, Sweden, US, Canada||0.01–0.17||<0.001–0.08||74.8–90.6||, , , , |
|Estradiol||China, France, Germany, Italy, Korea, Sweden, US||0.002–0.05||<0.001–0.007||92.6–100||, , , |
|Nonylphenol||China, France, Germany, Greece, Italy, Spain, US, Western Balkan Region||<0.03–101.6||<0.03–7.8||21.7–99||, , , , , ,|
|Bisphenol A||China, France, Greece, US, Western Balkan Region||<0.013–2.14||<0.03–1.10||62.5–99.6||, , , , , |
|Bis(2-ethylhexyl) phthalate (DEHP)||Austria, China, US||0.003–70.0||0.0001–54.0||25–97||, , |
2.2 Significant ECs in WWTP
There have some significant pharmaceuticals, EDCs, Personal Care products, antibiotics remains in WWTP effluents, which may cause negative effects but no specific reason has found against those contaminants. In recent years, researchers have shown an increased interest in monitoring ECs, but little studies exist on the list of substances that should be monitored . Some of the contaminants will be discussed which has significant concentrations found in wwtps influents.
Among the ECs that mixed in WWTPs influents are mainly the Medicine related contaminants in different countries data report and research. As orally consumed compounds containing potential contaminants are metabolized in human body and are subsequently excreted via urine and feces . For instance, ibuprofen was the amplest compound detected in the influent of four WWTPs in Spain and the concentration levels was ranging from 3.73 to 603 μg/L .
In Spain, WWTP secondary biological treatment plant effluent has been targeted 52 ECs, where 16 ECs consisted mainly of pharmaceuticals such as ibuprofen, hydrochlorothiazide, atenolol, diclofenac, ofloxacin, naproxen, trimethoprim, sulfamethoxazole. Those compounds are present at an initial concentration of over 750ng. L-1 and the effluent concentration the range of 80 gL-1 .
A wide range of EDCs can be removed by activated sludge process. Some of the EDCs are found in almost all the traditional WWTPs effluent. However, some tertiary treatment plants could gain a good percent of efficiency. Degradation by aerobic, anaerobic, and facultative digesters, ponds, lagoons, or bioreactors of different categories of ECs that anaerobic process for ECs degradation has been mostly studied in EDCs removal from activated sludge and the removal efficiencies ranged from 60 to 100% with high concentration of ECs  (Samaras et. al., 2013). Some of EDCs such as 17α-ethinyl estradiol, bisphenol A and nonylphenol have been found to show high removal efficiencies by aerobic biodegradation process. Primary treatment (sedimentation tank) also able to remove some EDCs with removal efficiency ranging from 13% to 43% .
2.2.3 Personal Care Products (PCPs)
The most common type of PCPs with high concentrations in activated sludge WWTP effluents found are 4-Chloroxylenol, Benzophenone-4, Triclosan, p-Benzylphenol, 4-Chloroxylenol.  and  respectively, where 88% and 93% degradation efficiency of triclosan was found during activated sludge treatment. Triclosan undergoes biodegradation but due to its relatively high partition coefficient (Kow ¼ 5.4), it is also adsorbed to sludge . 4-Chloroxylenol, p-Benzylphenol, Benzophenone-4, 4-Chloroxylenol also could not remove fully by conventional WWTP. And their removal efficiency was 33-83% .
3. Advanced Treatment Technologies
Ozone is a very powerful oxidant that reacts selectively with double bonds and aromatic rings of ECs with a high electron density . Ozone molecules involves direct reaction of ECs with the action of secondary oxidants such as hydroxyl radicals in aqueous solution . An ozone treatment system may increase the energy demand over a conventional WWTP by 40–50%. Pesticides, pharmaceuticals, and beta blockers were very successfully removed by up to 97–100% during ozonation in the presence of H2O2 at environmental relevant concentrations  (Rodríguez et. al., 2008).
3.2 Biological Activated Carbon (BAC) Filter
Activated carbon is generally use as an adsorbent and it is very popular to adsorb pollutants from media. Mechanism involves the interaction of granular activated carbon are microorganisms, particles, contaminants, and the dissolved oxygen in solution . However, activated carbon has limited adsorption capacity, whose further usage is to grow biological organism in its surface to retract adsorptive micropollutants, but sometimes can’t adsorb complex organisms. Overall, for the removal of ECs, it can say that biological activated carbon process followed the order of removal in aqueous media i.e. pesticides > beta blockers > pharmaceuticals > EDCs > PCPs .
3.3 Ozone- GAC Biological Filter
Last few years some of the application of hybrid system in wastewater treatment were performed to prevent the release of ECs into the aquatic environment via effluent discharge.Most of the hybrid systems consist of biological based treatment followed by some physical or chemical treatment systems. Chemical oxidation based treatment such as ozonation is the most widely used process to combine with biological activated carbon process. The removal efficiency for beta blockers by Ozone-GAC hybrid system is very effective than other hybrid treatment technologies. The general trend for the removal of beta blockers in aqueous medium is ozonation–biological activated carbon > MBR with reverse osmosis or nanofiltration or ultrafiltration > flocculation–activated sludge–ultrafiltration > constructed wetland .
Ozonation followed by biological activated carbon hybrid system has observed effectively remove pesticides, beta blockers and pharmaceuticals . Also, Other than that, a large list of EDCs can efficiently remove by Ozone- GAC Hybrid system. Biological sand filtration followed by ozonation has the potential to further removal of some organic compounds present at trace levels and reduce non-specific toxicity . On the other side, biological activated carbon (BAC) filtration has been used for many years in drinking water treatment, usually after ozonation, and is able to remove ozonation transformation products, natural organic matter, disinfection by-product precursors . In ozonation processes, there are two ways that the organic compounds can be oxidized: reaction with molecular ozone (direct pathway) and reaction with hydroxyl radical generated by ozone decomposition in water (indirect pathway). Molecular ozone reacts particularly with organic compounds and reaction rates vary over numerous orders of degree.
4. Removal of Different EC by BAC and Ozone-GAC biofilter
Several Pharmaceuticals, EDCs, Beta Blockers, PCPs, Pesticides were studied previously by several researchers with BAC and Ozone-GAC biofilter to remove from WWTPs effluents. Some ECs could remove efficiently but some couldn’t due to ECs structure and their chemical characteristics.
4. 1 Diclofenac
Diclofenac (DCF) is a non-steroidal inflammatory drug, used as an analgesic, to reduce inflammation in arthritis, rheumatic conditions and even to ease menstrual pain. Also, it can be found marketed as Flector patch, Voltarol, Voltaren, Diclo, etc. As literature reports, DCF is one of the pharmaceuticals most detected in water sources, it can be detected in influents and effluents from water treatment plants at concentrations up to µ/L level . Researches shows biological treatments seem to be inefficient on the degradation of this compound, being necessary the study of new technologies such advance oxidation processes (AOPs) to avoid the contamination of natural waters . Some of the WWTP operated by conventional biological treatments are barely remove this compound . According to table 2, the treated water which has been collected from WWTP and after the ozonation process, the effluent quality has improved at different Ozone dosage. Also, the pH plays a role to modify the contaminant towards decay.
Table 2: Removal of Diclofenac by ozonation of WWTP treated effluents
|Effluent type||DOC or TOC||pH||Temperature (°C)||O3 dosage||Removal Efficiency||References|
|Tertiary effluent||11.2||7±0.5||22±2||0.5 mg/mg DOC||> 94%|||
|Tertiary effluent||7.2||7.0||20||1 mg/mgTOC||98-99%|||
|Tertiary effluent||5.5||7.0||12-17||0.62 mg/mgDOC||98-100%|||
|Tertiary effluent||23.0||7.2||–||0.20 mg/mgDOC||>96%|||
|Tertiary effluent||7.2||7.0||20||0.36 mg/mgDOC||>99%|||
|3 effluents||6.6-10.3||7.1-8.2||18||0.20 mg/mgDOC||20-99%|||
|3 effluents||6.6-10.3||7.1-8.2||18||0.6 mg/mgDOC||>99%|||
|–||5.0 ± 1.5||–||10.3 ± 1.9 g m−3||~100|||
In Table 3, it shows the effluent of WWTPs which had higher concentration of diclofenac. During the treatment, they have followed the way of ozonation as a pretreatment purpose and after that the biofiltration, those contaminants broke down to a size, by which microorganisms could adsorb the remaining fraction that corresponds up to almost 100% of the treatment.
Table 3: Removal of Diclofenac by ozonation – biofilter
Naproxen is an anti-inflammatory drug commonly used to treat diseases and pain  also recently it has been detected in engineered and natural aquatic environments. Other investigators also reported that naproxen could be removed by biodegradation . However, According to Table 4, it shows due to the oxidation, Naproxen become more dividend and at Table 5, it shows that due to biodegradation the removal of Naproxen become more significant. Whether the influent concentration is, the removal efficiency of BAC and BAC- Ozone hybrid system were about 100%.
Table 4: Removal of Naproxen by ozonation of WWTP treated effluents
|Effluent type||DOC or TOC||pH||Temperature (°C)||O3 dosage||Removal Efficiency||References|
|Tertiary effluent||6.4±1.4||8.5||25||~0.35 mg/mg TOC||> 89%|||
|3 effluent||6.6-10.3||7.1-8.2||18||0.60 mg/mgDOC||>99%|||
|3 effluent||6.6-10.3||7.1-8.2||18||0.20 mg/mgDOC||20-99%|||
|Tertiary effluent||5.5||7.0||12-17||0.62 mg/mgDOC||59-98%|||
Table 5: Removal of Naproxen by ozonation – biofilter
|188.8- 345.8||NQ ~<1.6||99%|||
Atenolol (ATN), one of the most consumed beta blockers, is not fully metabolized by the human body and thus is excreted mostly (about 90%) unaltered through urine . So, atenolol (ATN) has been widely detected in hospital sewage and wastewater treatment in concentrations ranging from about from 0.78 mg L-1 to 6.6 mg L-1 . In relation to beta-blockers, the most studied compounds, such as atenolol, metoprolol and propranolol were frequently detected in the studied WWTP . Thus, amide and urea functional groups from compounds such as carbamazepine and atenolol were found to be biologically transformed through mediated hydrolysis reactions . So, before biological transformation, Atenolol with certain quantity of ozone dosage cause the production of transformation products and as a result it could adsorbed by microorganisms. From Table 6 and Table 7, it has the reflection of such statement. Due to ozonation, Atenolol has diminished most quantity but after that, using biofilter has gained more removal efficiency. The general trend for the removal of beta blockers is ozonation–biological activated carbon > MBR with reverse osmosis or nanofiltration or ultrafiltration > flocculation–activated sludge–ultrafiltration > constructed wetland .
Table 6: Removal of Atenolol by ozonation of WWTP treated effluents
|Effluent type||DOC or TOC||pH||Temperature (°C)||O3 dosage||Removal Efficiency||References|
|Tertiary effluent||11.2||7±0.5||22±2||~0.5 mg/mg DOC||40-93%|||
|Tertiary effluent||5.5||7.0||12-17||0.62 mg/mgDOC||55-92%|||
|3 effluent||6.6-10.3||7.1-8.2||18||0.60 mg/mgDOC||40-80%|||
|Tertiary effluent||6.4±1.4||8.5||25||~1.5 mg/mg TOC||>97%|||
4.4 Bisphenol A:
Bisphenol A is a common plasticizer, which is consumed in the formation of polycarbonate and epoxy resins. These are produced over 680,000 t/annum by the European Union . According to USEPA  investigations, BPA has taken on the Concern List as a substance that may present an unreasonable risk of injury to the environment based on its potential for long term adverse effects on growth, reproduction and development in aquatic species. Main reason to mix in water body at environment is domestic and industrial wastewater, and urban and agricultural runoff . Conventional WWTP can partially remove (43 ng L-1) Bisphenol A from influent water and both biological activated carbon and hybrid method of BAC- Ozone could achieve 78% efficiency . However, another research showed that, the mixing of Ozone with water for 60 mins and the regidor was 9.5 mg/L, as a result the removal efficiency was about 98% .
Several researches have occupied with Ibuprofen with BAC and BAC-Ozone hybrid treatment. Based on the
level of ozone dosage, the removal has varied, though the concentration of effluent water is lower. However, the
BAC removal efficiency was almost same in all the researches. Gerrity  studied with 31 contaminants, and
the ibuprofen removal has achieved satisfactorily in BAC filter, whether ozone could remove 83%. Where
ozone played a great role in removing this contaminant.
Table 8: Removal of Ibuprofen by ozonation – biofilter
|< 21.2- 87.5||1.4-4.7||80%|||
Sulfamethoxazole (utilized as a model bacteriostatic anti-microbial) is persevering to customary natural medications of wastewaters. At any dosage of ozone that would mix with water may exhaust almost completely of Sulfamethoxazole from water. Further filtration with GAC biofilter of those water may purify of that EC. Moreover, tertiary effluents may cause small reduction of removal than 3 effluent, this is the case for ozonation. However, during filtration, removal percentage was almost same.
Table 9: Removal of Sulfamethoxazole by ozonation of WWTP treated effluents
|Effluent type||DOC or TOC||pH||Temperature (°C)||O3 dosage||Removal Efficiency||References|
|Tertiary effluent||11.2||7±0.5||22±2||0.5 mg/mg DOC||> 93%|||
|3 effluent||6.6-10.3||7.1-8.2||18||0.60 mg/mgDOC||>99%|||
|3 effluent||6.6-10.3||7.1-8.2||18||0.20 mg/mgDOC||20-99%|||
|Tertiary effluent||5.5||7.0||12-17||0.62 mg/mgDOC||92-98%|||
According to Table 10, ozonation biofilter did a significant performance in removing Sulfamethoxazole, though the influent concentration is too low. But in Table 9, it shows, ozone removed majorities of contaminants by break down. Also, dosage played a great role, where removal depends on it.
Table 10: Removal of Sulfamethoxazole by ozonation – biofilter
This is a pharmaceutical compound which has significant amounts in wwtp effluents as well as in the effluents of advanced treatments. They can’t achieve significant removal due to the limited biodegradability of biofilters . However, the ozonation could remove about 78% which is the moderate quantity. The influent water of wwtp was 15.7 ± 3.8 μg L−1, whose remaining concentration was 1.9 ± 0.7 μg L−1 for Ozonation and 1.2 μg L−1 was for Ozonated-GAC biofilter . Also, according to Gurke , conventional WWTP’s can’t remove significant quantity of Gabapentin from influents water. Where influents were 13.2 ±3.3 μg/L and effluents concentrations were 12.1 ±2.6 μg/L. So, this compound may have complex bonding structures to break by microorganisms.
According to the Knopp , there were no removal of compounds by sludge treatment in WWTP, but by Ozonation and GAC biofilter, the quantities has removed completely. Also, according to , Ozone-GAC biofilter could remove significant quantities of Carbamazepine which is in the range of 82-95%. Carbamazepine influent concentration got lower and also the removal efficiency by Ozone and GAC also very effective .
Table 11: Removal of Carbamazepine by Ozone and Ozonation – GAC biofilter
|Influent Conc. of WWTP (μg/L)||Effluent Conc. of WWTP (μg/L)||Ozone Effluents (μg/L)||Ozone-GAC biofilter Effluents (μg/L)||References|
|1.3 ± 0.3||1.4 ± 0.3||<LOQ||<LOQ|||
5. Future Research Prospects:
From this studied paper, it can see that for pharmaceuticals, beta blockers, EDCs, it can have some compounds that can completely remove or moderately remove by Ozonation- biofilter hybrid system. The conventional WWTPs with certain mixing quantity of ozone and then biological removal could effectively remove such untreated ECs. Matamoros  suggested after several researches that, combined use of different biologically based WW treatments aided to increase compounds’ elimination. That means only biological process could barely remove some complex structured compounds but after the combined treatment and then biological treatment may leads more removal percentage. Prospects are:
- All characteristical assumption for EC in several researches mentioned that, due to unavailable information to identify the specific removal procedure, it can’t get properly.
- Sampling procedure, operating parameters may certainly responsible for the removal percentage of ECs.
- To get full scale of effectiveness from the Ozone- Biofiltration, it should have done with trial by examining its sustainability, whether it is feasible or not.
Biological treatment has mainly good percentage removal on the field of pharmaceuticals and some of other categories of ECs according to several researches. So, only biological treatment like biofiltration can deal with good efficiency in certain quantity of compounds. But instead of this, combined treatment techniques could have get high efficiency once the transformation product has produced due to ozonation or advanced treatment. That breaks down and easily adsorb by microscopic microorganisms. For getting more removal efficiency, pretreatment, and post treatment before and after biofiltration plays a great role in removal of complex compounds from WWTPs effluents. Overall, it can say that as much advanced treatment with proper techniques apply during treatment, it is able to obtain good removal quantity of complex compounds.
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