Biofilter Research Articles

Enhancing the biodegradation of hydrophobic volatile organic compounds: A study on microbial consortia adaptation and the role of surfactants

The emission of hydrophobic Volatile Organic Compounds (VOCs) is a serious environmental issue. Typically, biofilters (BFs) are employed for their treatment, with the potential enhancement of mass transfer through the addition of surfactants. However, disparate results in previous studies have been observed, attributed to uncontrolled conditions during the introduction of surfactants to BFs. Additionally, there has been limited exploration of microbial consortium adaptation to surfactants. To address these gaps, this study followed two approaches. First, the long-term (247 days) removal of cyclohexane was studied in a stirred tank bioreactor (STBR) inoculated with Rhodococcus erythropolys E1 and using Tween 80 at three times the critical micelle concentration (CMC). Second, the short-term (9 days) impact of two (bio)surfactants [Tween 80 (1 × CMC) and Quillaja Saponin (QS, 1 × CMC)] on the removal of cyclohexane, hexane and toluene was investigated in batch tests using three types of inocula: a pure culture of Rhodococcus erythropolys E1 (X0), a microbial consortium adapted to cyclohexane (X1), and a microbial consortium adapted to cyclohexane with Tween 80 (X2). For long-term operation, the addition of Tween 80 at 3 × CMC improved cyclohexane removal efficiency (RE) to 87 ± 1% (elimination capacity, EC = 145 ± 25 mg m−3 h−1, gas residence time, GRT = 20 min, inlet concentration, Cin = 14.9 ± 2.5 ppmv), compared to a RE of 32 ± 9% (EC = 44 ± 8 mg m−3 h−1, GRT = 20 min, Cin = 15.1 ± 0.7 ppmv) under similar conditions without surfactants. For short-term operation, the addition of QS at 1 × CMC significantly increased biomass growth, resulting in lower maximum specific consumption rates for X1 and X2 compared to scenarios without surfactants or 1 × CMC Tween 80. The most abundant genera in X1 and X2 were Paludisphaera (26-23%), 67-14 genus (17–23%), and Rhodococcus (9–18%), respectively.

Sea Vegetables: An Alternative Food Source: A Review

Seaweeds or sea vegetables are the non-traditional vegetables largely produced and consumed by China, Japan, Korea, Indonesia, Philippines, Malaysia, Vietnam and other island countries. They are rich in essential nutrients, including minerals, vitamins, amino acids etc. making them a valuable addition to a balanced diet. Moreover, they have low caloric content and are free from cholesterol, essential for weight management and heart-healthy diets. Additionally, sea vegetables contain unique bioactive compounds such as polysaccharides, polyphenols and omega-3 fatty acids, which have antioxidant, anti-inflammatory and anti-cancer properties. Globally the demand for seaweed as vegetables along with its several value-added products are increasing day by day. The cultivation of seaweed is cost effective as it does not require seeds, fertilizers, pesticides, no freshwater and arable land. Sea vegetables can serve as bio filters by absorbing excess nutrients from aquatic ecosystems, thus promoting environmental sustainability in coastal aquatic system. To combat hunger, achieve food security and protect the environment, it is crucial to create public awareness on the health benefits and nutritional value of sea vegetables. More in-depth research and developments are required to commercialize, explore the diversity of sea vegetables, develop innovative culinary applications and establishment of quality and safety standards. The present review works highlights a comprehensive overview of seaweed diversity, nutritional composition, health benefits, diverse uses, cultivation methods and potential for developing processed products for food and agricultural industry.

Vermifiltration for removal of emerging contaminant EDTA (ethylenediaminetetraacetic acid). Kinetics models for adsorption, bio- and vermidegradation

Vermifiltration is a sustainable technology that combines the action of microorganisms and earthworms to remove contaminants in wastewater. In this work, vermifiltration was used to remove the emerging contaminant, EDTA, from simulated greywater. Three types of filters were designed: Azide Filter (AF) to evaluate the adsorption process, Bio filter (BF), to evaluate adsorption plus the action of the microorganisms, and Vermi Filter (VF), to assess the previously described processes and the action of the earthworms. Each filter was filled with gravel, sand and an active layer, and VF was inoculated with 60 Eisenia fetida. The filters were operated on a batch system with recycling. Different regimes were observed: an initial rapid decrease of EDTA concentration by adsorption; a lag phase, which lasted from 7 to 18 days, and a final EDTA decrease due to biological or vermi degradation. A mathematical model was developed performing the EDTA mass balance in the system and considering a first order kinetic rate for EDTA removal. Experimental data was fitted by the model, determining kinetic constants for adsorption or degradation process, kads and kd respectively. The kads values were similar for all filters, whereas VF showed a kd 53 % higher than that of BF and AF. Earthworms survival was 85 % and, although the biomass was significantly reduced (64.8 %), there was cocoons and juveniles. Bioassays with Lactuca sativa showed no phytotoxicity of the treated wastewaters. All the systems were efficient but the VF was faster, supporting that vermifiltration is a suitable technology for treating EDTA greywater.

Effect of toluene on siloxane biodegradation and microbial communities in biofilters

The removal of volatile methyl siloxanes (VMS) from landfill biogas is crucial for clean energy utilization. VMS are usually found together with aromatic compounds in landfill biogas of which toluene is the major representative. In the present study, two biofilters (BFs) packed with either woodchips and compost (WC) or perlite (PER) were used to study the (co–) removal of octamethyltrisiloxane (L3) and octamethylcyclotetrasiloxane (D4) from gas in presence and absence of toluene, used as a representative aromatic compound. The presence of low inlet toluene concentrations (315 ± 19 – 635 ± 80 mg toluene m-3) enhanced the VMS elimination capacity (EC) in both BFs by a factor of 1.8 to 12.6. The highest removal efficiencies for D4 (57.1 ± 1.1 %; EC = 0.12 ± 0.01 gD4 m-3 h-1) and L3 (52.0 ± 0.6 %; EC = 0.23 ± 0.01 gL3 m-3 h-1) were observed in the BF packed with WC. The first section of the BFs (EBRT = 9 min), where toluene was (almost) completely removed, accounted for the majority (87.7 ± 0.6 %) of the total VMS removal. Microbial analysis revealed the impact of VMS and toluene in the activated sludge, showing a clear selection for certain genera in samples influenced by VMS in the presence (X2) or absence (X1) of toluene, such as Pseudomonas (X1 = 0.91 and X2 = 12.0 %), Sphingobium (X1 = 0.09 and X2 = 4.04 %), Rhodococcus (X1 = 0.42 and X2 = 3.91 %), and Bacillus (X1 = 7.15 and X2 = 3.84 %). The significant maximum EC values obtained by the BFs (0.58 gVMS m-3 h-1) hold notable significance in a combined system framework as they could enhance the longevity of traditional physicochemical methods to remove VMS like activated carbon in diverse environmental scenarios.

Evaluation of Chaetoceros Sp. microalgae bio filters efficiency in urban wastewater treatment

Evaluation of Chaetoceros Sp. microalgae bio filters efficiency in urban wastewater treatment

Synthetic greywater treatment using a scalable granular activated carbon bioelectrochemical reactor

Greywater reuse has emerged as a promising solution for addressing water shortages. However, greywater needs treatment before reuse to meet the required water quality standards. Conventional wastewater treatment technologies are unsuitable for recreating highly decentralized domestic greywater. This study evaluated bioelectrochemical reactors (BERs) with granular activated carbon (GAC) as a sustainable alternative for developing decentralized and low-cost biological treatment systems. BERs using GAC as the anode material and conventional GAC biofilters (BFs) for synthetic greywater treatment were operated in batch mode for 110 days in two stages: (i) with polarized anodes at −150 mV vs. Ag/AgCl and (ii) as a microbial fuel cell with an external resistance of 1 kΩ. Anode polarization produced an electrosorption effect, increasing the ion removal of the BERs. Power production during the operation and cyclic voltammetry tests of the extracted granules revealed electrochemically active biofilm development on the BERs. Although low power density (0.193 ± 0.052 µW m−3) was observed in BERs, they showed a similar performance in sCOD removal (BER = 91.6–89.6 %; BF = 96.2–93.2 %) and turbidity removal (BER = 81–82 %; BF = 30–62 %) to BFs that used 50 % aeration. Additionally, scanning electron microscopy of sampled granules showed higher biomass formation in BER granules than in BF granules, suggesting a higher contribution of sessile (vs. planktonic) cells to the treatment. Thus, the results highlight the synergistic removal effect of the GAC-based BER. The scalable design presented in this study represents a proof-of-concept for developing BERs to use in decentralized greywater treatment systems.

Optimization of on-site wastewater treatment efficiency and recovery based on nutrient mobility and adsorption kinetics modelling using HYDRUS-2D coupled with PHREEQC

A closed-loop on-site wastewater treatment system (OWT) was studied comprising steps of septic tank to remove organics (Biological Oxygen Demand (BOD)), biofiltration clarifier for biological removal of nitrogen (N), phosphorus (P) and BOD, reactive Polonite® filter for chemical adsorption and precipitation removal of dissolved P, and tidal flow constructed wetland (TFCW) sand filter for polishing the effluent to low P and N effluent Swedish standards. The field experimental data that have been used to optimize TFCW design in the numerical modelling using HYDRUS-2D coupled with and without PHREEQC indicated that the adsorption efficiency of the reactive Polonite® adsorbent was nearly double to that obtained in TFCW sand filters for PO4-P (95 %) and Total-P (85 %) removal in summer at a high temperature range (15.4–18.8 °C) and pH range (9.9–10.8). The weaker PO4-P (53 %) and Total-P (25 %) removal efficiency in winter was due to a low temperature (1.5–8.1 °C) and low pH (7.2–7.9). This decrease in pH was attributed to salinity in the domestic wastewater and dilution of rainwater. Modelling results revealed that the transport mechanisms and rate of P adsorption kinetics in the TFCW sand filters enhanced with calcium and iron flow from chemical dissolution in the preceding Polonite® adsorbent was increased with the increase in temperature. However, the P adsorption was less sensitive at high ferrihydrite (Fe(OH)3) dose, suggesting limited effects of cations dissolution and abundance of metal oxides and hydroxide ions at the mineral surface for anions exchange with phosphate for surface complexation. The strategy of combining field data and modelling provided valuable insights for assessing adaptability and optimizing TFCW design under variable fluxes and scenario effects of insulated/uninsulated and dilution by rainwater in cold-climate regions.

Evaluación de la eliminación de carbamazepina de aguas residuales de hospital en un biofiltro no convencional y aplicación de electro-oxidación como pretratamiento

Hospital wastewater (HWW) is characterized by a high drug concentration, which can cause endocrine effects and bacterial resistance, among others. For this study, carbamazepine (CBZ) was selected as a contaminant model to evaluate the removal efficiency from HWW of recalcitrant pharmaceuticals in a non conventional biofilter (BF), packed with a mixture of wood chips (Prosopis) and porous rock (pouzzolane). The effect of electro-oxidation (EO) as pre-treatment was assessed as well. A biofilm adapted to the HWW was developed in the BF. The addition of high concentrations of CBZ (1 000 and 10 000 µg/l) to the influent HWW did not affect the removal efficiency of the BF to remove organic matter (73 %) and ammonia nitrogen (99 %), proving that the biomass was not inhibited by the CBZ’s concentration. The BF showed a significant removal of CBZ by adsorption during the start up. The bed filter showed an adsorption capacity of 19.84 µg/g (Co = 10 000 µg/l). After the bed filter saturation operated in steady state, the BF removed by biotransformation 17.2 ± 7.4 % of CBZ which, in terms of concentration (1 551 ± 664 µg/l), is bigger than the concentration in most of the reports for hospital, pharmaceutical and municipal WW effluents, which are between 0.1 and 890 µg/l. By applying electro-oxidation as a pretreatment, the global removal efficiency of CBZ increased to 55 ± 5.96 %. In the hybrid system, the EO biotransformed the CBZ, and in the BF the nitrogen and the COD were removed and showed CBZ desorption.

Assessing macroscopic and microscopic performance of fungal-based biofilters for methane abatement

Fungi have recently been shown to increase the performance of biofiltration in removing hydrophobic compounds like methane (CH4). The effectiveness of fungal-based biofiltration for treating low-concentrated (2% v/v) CH4 emissions was assessed in three biofilters (BFs) packed with expanded clay or compost and inoculated with fungal strains. The BFs were operated under different conditions of empty bed residence time (EBRT), pH of the mineral medium and irrigation. No CH4 removal was recorded in the BF inoculated with Candida subhashii and packed with expanded clay. Similarly, low CH4 abatement performances were observed for BF-1 and BF-2 inoculated with Fusarium solani and packed with expanded clay, with maximum removals of ∼36% when irrigated with MSM at a pH of 7 and operated at an EBRT of 42 min. Opposite, BF-3 packed with compost and inoculated with F. solani achieved average removals ranging from 80.3% (EC of 19 g m−3 h−1) at an EBRT of 34 min to 52.0% (EC of 22 g m−3 h−1) when decreasing the EBRT to 18 min. Amplicon metagenomics showed that CH4-degrading bacteria natural of compost were representative in BF-3. It also showed the importance of biostimulation in biofiltration for promoting methanotrophic growth. The fungal characterization revealed that a key factor on fungal BFs is the dominant fungi present. In this sense, Fusarium and clade LKM11 promoted methanotrophic growth. This knowledge can be applied to the operation of fungal BFs subjected to the treatment of CH4 via controlled bioaugmentation and biostimulation.

Effect of surfactant addition on the biofiltration of siloxane-contaminated gas streams

Biogas contains low levels of volatile methyl siloxanes (VMS), which are responsible for severe damage to turbines or internal combustion engines during energy recovery. In this study, we investigated the removal of the linear octamethyltrisiloxane (L3) and cyclic octamethylcyclotetrasiloxane (D4) from gas by using two biofilters (BFs) filled with either woodchips and compost (WC) or perlite (PER). To overcome the mass transfer limitation, the addition of a synthetic (Tween 80) and a biological (Quillaja saponin, QS) surfactant on the removal of VMS in both BFs was studied. Tween 80 (added at × 1 critical micelle concentration, CMC) and QS (also at × 1 CMC) enhanced VMS removal in both BFs. Specifically, the performance of both BFs increased from an average VMS elimination capacity (EC) of 0.07 ± 0.04 g VMS m−3 h−1 to 0.24 ± 0.08 g VMS m−3 h−1 (Tween 80) and 0.43 ± 0.02 g VMS m−3 h−1 (QS). However, higher concentrations of Tween 80 ( × 3 CMC) did not further improve VMS removal. The WC BF exhibited a higher maximum EC of 0.63 g VMS m−3 h−1 (0.37 g D4 m−3 h−1 and 0.26 g L3 m−3 h−1), with a VMS RE of 28.4 ± 2.0% (D4 RE = 30.4% and L3 RE = 26.5%). The PER BF obtained a maximum EC of 0.52 g VMS m−3 h−1 (0.28 g D4 m−3 h−1 and 0.23 g L3 m−3 h−1), along with a VMS RE of 32.0 ± 0.8% (D4 RE = 31.2% and L3 RE = 32.8%). The most abundant genera in the WC BF were Mycobacterium (7.5–1.8%), Rhodococcus (1.1–7.2%), and Planctomicrobium (5.1–2.9%). However, given the high microbial diversity present in WC BF and the complex structure of VMS, their removal was most likely due to the joint activity of several microorganisms with VMS-degrading capacity, such as Bacillus (0.58–0.39%), Pseudomonas (0.07–0.04%), Dokdonella (0.50–0.10%), Microbacterium (0.5%), Novosphingobium (0.02%), Gordonia (0.5–0.1%), and Sphingopyxis (0.07%).

Effect of inoculum type, packing material and operational conditions on the biofiltration of a mixture of hydrophobic volatile organic compounds in air

The emission of volatile organic compounds (VOCs) into the atmosphere causes negative environmental and health effects. Biofiltration is known to be an efficient and cost-effective treatment technology for the removal of VOCs in waste gas streams. However, little is known on the removal of VOC mixtures and the effect of operational conditions, particularly for hydrophobic VOCs, and on the microbial populations governing the biofiltration process. In this study, we evaluated the effect of inoculum type (acclimated activated sludge (A-AS) versus Rhodococcus erythropolis) and packing material (mixture of compost and wood chips (C + WC) versus expanded perlite) on the removal of a mixture of hydrophobic VOCs (toluene, cyclohexane and hexane) in three biofilters (BFs), i.e., BF1: C + WC and R. erythropolis; BF2: C + WC and A-AS; and BF3: expanded perlite and R. erythropolis. The BFs were operated for 374 days at varying inlet loads (ILs) and empty bed residence times (EBRTs). The results showed that the VOCs were removed in the following order: toluene > cyclohexane > hexane, which corresponds to their air-water partitioning coefficient and thus bioavailability of each VOC. Toluene is the most hydrophilic VOC, while hexane is the most hydrophobic. BF2 outperformed BF1 and BF3 in each operational phase, with average maximum elimination capacities (ECmax) of 21 ± 3 g toluene m−3 h−1 (removal efficiency (RE): 100 %; EBRT: 82 s), 11 ± 2 g cyclohexane m−3 h−1 (RE: 86 ± 6 %; EBRT: 163 s) and 6.2 ± 0.9 g hexane m−3 h−1 (RE: 96 ± 4 %; EBRT: 245 s). Microbial analysis showed that despite having different inocula, the genera Rhodococcus, Mycobacterium and/or Pseudonocardia dominated in all BFs but at different relative abundances. This study provides new insights into the removal of difficult-to-degrade VOC mixtures with limited research to date on biofiltration.

Optimization pilot scale study on ammonia nitrogen removal by bio filter

In order to obtain the optimal conditions for ammonia nitrogen (AN) wastewater treatment by bio filter (BF), the effects of ratio of carbon to nitrogen (C/N), pH, and hydraulic load (HL) on the AN degradation were studied by Response Surface Methodology (RSM). Central Composite Design (CCD) experiments were conducted, and the response of the AN removal rates were fitted to a second-order polynomial model. The analysis of variance showed that the model was accurate and reliable. Through model fitting, the optimal condition for AN removal was: C/N of 18.95, pH of 7.78, and HL of 1.04 d−1. The maximum AN removal rate predicted by the model was 91.90%, accorded with the experimental verification value of 91.37% under the optimal condition. The research provided valuable demonstration for optimizing process parameters on AN removal in BF.

Selection of Wastewater Treatment Technology: AHP Method in Multi-Criteria Decision Making

Wastewater treatment is a process that reduces pollution to those quantities and concentrations at which purified wastewater is no longer a threat to human and animal health and safety and does not cause unwanted changes in the environment. Municipal wastewater is classified as biodegradable water. Special importance should be given to wastewater with a high content of organic matter (COD), phosphorus (P) and nitrogen (N). MBBR technology, developed on the basis of the conventional activated sludge process and the bio filter process, does not take up much space and does not have problems with activated sludge, as in the case of conventional biological reactors, and has shown good results for the removal of organic matter, phosphorus and nitrogen. The aim of this paper is to optimize the wastewater treatment process in the municipality of Dojran, North Macedonia. Three alternative solutions for improving the capacity for wastewater treatment in the municipality of Dojran were analyzed. The shortlist of variants was made on the basis of several criteria, including: analysis of the system in the tourist season and beyond, assessment of the condition and efficiency of the existing wastewater treatment plant (WWTP) in combination with a new treatment plant, treatment efficiency when using different wastewater treatment technologies, the size of the site needed to accommodate the capacity, as well as the financial parameters for the proposed system. The selection of the most favorable solution for the improvement of the wastewater treatment system was made using the AHP (analytic hierarchy process) method. In order to select the optimal solution, a detailed analysis was conducted, considering several decision-making criteria, namely the initial investment, operating costs and management complexity. Based on the obtained results, Variant 3 was recommended, that is, the construction of a completely new station with MBBR technology, with a capacity for 6000 equivalent inhabitants.

Effects of filling methods on the degradation of ethyl acetate and the microbial community in biofilters

Two biofilters (BFs) for treating ethyl acetate (EA) were constructed with magnetite, activated carbon, perlite and gravel added via layered filling (BF1) or mixed filling (BF2). This study demonstrated the effect of filling method on the degradation of EA and the microbial community in the BFs. The results indicated that the EA removal efficiency (RE) of BF1 and BF2 reached 86.3 ± 3.0 % and 88.9 ± 2.1 %, respectively, under low inlet load (L-IL; (224 g/(m3·h)). Meanwhile, BF2 exhibited stabler RE than BF1 at high IL. BF1 achieved the highest REs of total phosphorus (TP), total nitrogen (TN) and ammonia nitrogen (NH4+-N) under moderate inlet load (M-IL; 336 g/(m3·h)), with average values of 95.8 ± 3.5 %, 83.4 ± 0.4 %, and 85.7 ± 0.3 %, respectively. The removal of TP, TN and NH4+-N in BF2 was superior than BF1 at L-IL and M-IL condition. Moreover, the genera Burkholderia, Acinetobacter, unclassified_Rhizobiales and unclassified_Burkholderiales were the dominant EA-degrading bacteria in BF1, while the EA-degrading bacteria in BF2 were dominated by unclassified_Chloroflexi, unclassified_Bacteroidetes and unclassified_Anaerolineaceae. Furthermore, the mechanism investigation of the mechanism revealed that the types of filling method affect EA degradation by shifting the abundance and diversity of key microorganisms in biodegradation. This study provides an effective strategy for improving the biodegradation efficiency of volatile organic compounds VOCs.

Some Physical Properties and Bacteriological Evaluation of Raw Landfill Leachate from Gosa Landfill in the Federal Capital Territory, Abuja, Nigeria

The physical and bacteriological evaluation of raw landfill leachate from Gosa Landfill in FCT, Abuja, Nigeria was carried out in this study using standard procedures. The probable bacteria identified from the biochemical tests of isolated samples were Streptococcus pneumoniae with Pseudomonas aeruginosa and Staphylococcus aureus. However, molecular characterization involving sequencing and BLAST further confirmed the bacteria present. This study concludes that the bio filter produced from Coco peat and Ash affects both the physicochemical properties and bacteriological flora of raw landfill leachate through degradation.

An alternative approach towards nitrification and bioremediation of wastewater from aquaponics using biofilm-based bioreactors: A review

Aquaponics combines the advantages of aquaculture and hydroponics as it suits the urban environment where a lack of agricultural land and water resources is observed. It is an ecologically sound system that completely reuses its system waste as plant fertilizer. It offers sustainable water savings, making it a supreme technology for food production. The two major processes that hold the system together are nitrification and denitrification. The remains of fish in form of ammonia reach the bio filters where it is converted into nitrite and further into nitrate in presence of nitrifying and denitrifying bacteria. Nitrate eventually is taken up by the plants. However, even after the uptake from the flow stream, the effluent contains remaining ammonium and nitrates, which cannot be directly released into the environment. In this review it is suggested how integrating the biofilm-based bioreactors in addition to aquaculture and hydroponics eliminates the possibility of remains of total ammonia nitrogen [TAN] contents, leading to bioremediation of effluent water from the system. Effluent water after releasing from a bioreactor can be reused in an aquaculture system, conditions provided in these bioreactors promote the growth of required bacteria and encourages the mutual development of plants and fishes and eventually leading to bioremediation of wastewater from aquaponics.

Particulate Matter Phytoremediation Effectiveness of Japanese Prunus × Yedoensis Tree Through Spring and Summer Season

Using green biofilters can help eliminate air pollutants and improve urban air quality. In the current study, Prunus × Yedoensis capacity of phytoremediation was investigated as a bio filter of Particulate matter (PM) in spring and summer seasons in Japan. Two samples were analysed to extract three fractions of PM (coarse, fine and ultra-fine). Results showed lower deposition of PM in spring season with total of 20.2 μg.cm-2 and high proportion for fine fraction (2.5-10μm), comparing with summer season which showed a higher deposition of PM with total of 31.9 μg.cm-2. Ultra-fine fraction (0.2–2.5μm) recorded the highest values with a percentage of 23.9% of the total PM deposition. Leaf micromorphological characteristics such as, rough surface and serrated margin can enhance the Prunus × Yedoensis ability of particulate matter accretion. This study confirms that vegetation has an efficient role in improving the quality of urban air. Further structural analysis should be included to deepen the understanding of phytoremediation phenomena in plants.

Fungal co-culture improves the biodegradation of hydrophobic VOCs gas mixtures in conventional biofilters and biotrickling filters

The present study systematically evaluated the potential of Candida subhashii, Fusarium solani and their consortium for the abatement of n-hexane, trichloroethylene (TCE), toluene and α-pinene in biofilters (BFs) and biotrickling filters (BTFs). Three 3.2 L BFs packed with polyurethane foam and operated at a gas residence time of 77 s with an air mixture of hydrophobic volatile organic compounds (VOCs) were inoculated with C. subhashii, F. solani and a combination of thereof. The systems were also operated under a BTF configuration with a liquid recirculating rate of 2.5 L h-1. Steady state elimination capacities (ECs) of total VOCs of 17.4 ± 0.7 g m−3 h−1 for C. subhashii, 21.2 ± 0.8 g m−3 h−1 for F. solani and 24.4 ± 1.4 g m−3 h−1 for their consortium were recorded in BFs, which increased up to 27.2 ± 1.6 g m−3 h−1, 29.2 ± 1.9 g m−3 h−1, 37.7 ± 3.3 g m−3 h−1 in BTFs. BTFs supported a superior biodegradation performance compared to BF, regardless of the VOCs. Moreover, a more effective VOC biodegradation was observed when C. subhashii and F. solani were grown as a consortium. The microbial analysis conducted revealed that the fungi initially introduced in each BF represented the dominant species by the end of the experiment, with C. subhashii gradually overcoming F. solani in the system inoculated with the fungal consortium.

Performance and neural modeling of a compost-based biofilter treating a gas-phase mixture of benzene and xylene

Biofilter (BF) has been regarded as a versatile gas treatment technology for removing volatile organic compounds (VOCs) from contaminated gas streams. In order for BF to be utilized in the industrial setting, it is essential to conduct research aimed at removing VOC mixtures under different inlet loading conditions, i.e. as a function of the gas flow rate and inlet VOC concentrations. The main aim of this study was to apply artificial neural networks (ANN) and determine the relationship between flow rate (FR), pressure drop (PD), inlet concentration (C), and removal efficiency (RE) in the BF treating gas-phase benzene and xylene mixtures. The ANN model was trained and tested to assess the removal efficiency of benzene (REB) and xylene (REX) under the influence of different FR, PD and C. The model's performance was assessed using a cross-validation method. The REb varied from 20% to >60%, while the REx varied from 10% to 70% during the different experimental phases of BF operation. The causal index (CI) technique was used to determine the sensitivity of the input parameters on the output variables. The ANN model with a topology of 4-4-2 performed the best in terms of predicting the RE profiles of both the pollutants. Furthermore, the effect was more pronounced for xylene because an increase in the benzene concentration reduced xylene removal (CI = −25.7170) more severely than benzene removal. An increase in the xylene concentration had a marginally positive effect on the benzene removal (CI = +0.1178).

Influence of pH, N, P, N: P Ratio, and Dissolved Inorganic Carbon on Ulva ohnoi Growth and Biomass Quality: Potential Implications in IMTA-RAS

Ulva ohnoi has a big potential in IMTA-RAS fish–seaweed systems. In order to design the best production strategy in these systems, the effect of the main environmental factors, such as pH, nutrient concentration (N, P, and N: P ratios) and dissolved inorganic carbon (DIC), on the productivity, bio filtration capacity, and quality of the biomass obtained was studied. It is concluded that in closed systems, strong pH variations (7.9–10.1) do not influence the growth of U. ohnoi and growth is slowed down due to the depletion of DIC. This fact would not be a problem in IMTA-RAS fish–macroalgae systems, due to the physiological activity of the fish contributing CO2 to the medium and replenishing it. The results obtained in the wide range of N: P ratios tested (2–410), allow us to conclude that this ratio should not be a limiting factor for the cultivation of Ulva ohnoi in IMTA-RAS systems. Based on those results, the best strategy to follow in an IMTA-RAS sole–sea lettuce would be to maintain the algae with highest level of nitrogen. This procedure implies a high rate of water renewal, which would also guarantee the maintenance of an adequate DIC and the best commercial quality of seaweed.