Trickling Filter Research Articles

Effect of Hydraulic and Organic Load, in the Removal of Biochemical Oxygen Demand in Wastewater using Biofilter with Vegetable Carbon, in High Andean Climate

Generating new sustainable alternatives in the design of trickling filters for rural populations is necessary to improve the quality of discharges and optimize the design of secondary treatment units. The study determined the impact of hydraulic and organic charge on the removal of BOD in the environment charcoal biofilter. Biofilters prototypes were implemented at scale with charcoal filter medium on different surfaces that vary from 0.12 to 0.25 m2, carried out at an elevation of 2100 meters above sea level, the final concentration most effective in removing BOD obtained hydraulic load of 2.34 to 4.76 m3m−2d−1 and the organic load between 0.27 to 0.56 kg DBO m−3. The results of the Biofilter experiments determined that the hydraulic load generated a better distribution and mixing of the residual water throughout the trickling bed, achieving a good reaction and effective combination between the water that entered and the amount of air required to complete the aerobic process. and to achieve the removal of BOD, the organic load obtained in the measurements concentrates enough biomass that helps in the formation of the biofilm, for which it is concluded that this criterion has a determining effect on the reduction of organic matter in domestic wastewater, it is confirmed that the charcoal biofilter is efficient and can be used in small systems of wastewater treatment plants.

Enhanced ex-situ biomethanation of hydrogen and carbon dioxide in a trickling filter bed reactor

Ex-situ biomethanation is an emerging technology used for converting carbon dioxide (CO2) and renewable hydrogen (H2) into biomethane. The aim of this study was to investigate the influence of 4:1 and 6:1 stoichiometric H2:CO2 ratio for converting simultaneously exogenous and endogenous CO2 to natural gas quality (biomethane) in the trickling filter bed (TFB) reactor. The coupling of H2 and CO2 produced methane (CH4) content up to 75% and 98% at 4:1 and 6:1 H2:CO2 ratio, respectively. At 6:1 H2:CO2 ratio, the reactor demonstrated its potential to meet the criteria for natural gas quality biomethane and produced CH4 at a rate up to 2.65 L/LR.d with complete H2 utilization. Samples collected from the inoculum, the biofilm formed on the carrier material, and the liquid phase of the reactor showed distinct changes in the microbial community composition. The significant increase in relative abundance of Methanoculleus bourgensis upon H2 injection indicates hydrogenotrophic methanogenesis as the main pathway for enhanced biomethanation. Thus, our study provides a novel approach for simultaneous utilization of CO2 and digestate in a single-stage TFB reactor for achieving higher CH4 content in the output gas.

Effect of trickling filter on carbon and nitrogen removal in vertical flow treatment wetlands: A full-scale investigation

Vertical Flow Treatment Wetland (VF-TW) systems achieve high efficiencies in terms of carbon related parameters removals from domestic wastewaters. Nitrogen removal is also efficient but optimisations are still needed. This article reports and discusses experimental data collected from 24-h monitoring campaigns of 29 full-scale VF-TWs, having different configurations and operation time up to 13 years. All monitored systems gathered 1 or 2 stage(s) of unsaturated or partially saturated VF-TW. Additionally, some of those included an aerobic biological Tricking Filter (TF) prior to TW stage(s). Results firstly showed that the implementation of a TF improved TSS, COD and BOD5 removal rates in the monitored systems. Regarding nitrogen removal, the association of TF with one stage of partially saturated vertical TW was found to achieve around 79% of nitrification in average and up to 92% in some cases. In the configurations where TF was associated to 2 successive stages of TW, almost all total nitrogen removal by nitrification/denitrification was achieved at the outlet of the first-stage TW. The contribution of the second-stage TW in denitrification was found very low due to limited availability of organic carbon to support heterotrophic denitrification. Specific solutions to enhance the contribution of the second stage in the denitrification process are discussed.

In-situ biogas upgrading in an anaerobic trickling filter bed reactor treating a thermal post-treated digestate

Digestate, residual organic matter produced as byproducts during the anaerobic digestion process, needs to be utilized because of its potential greenhouse gas emissions. An alternative solution is to valorize digestate for biogas production. The current study investigates feasibility of simultaneous thermal post-treatment of digestate and in-situ biogas upgrading in the trickling filter bed (TFB) reactor. Thermal post-treatment improved the solubilization of food waste-based digestate for biogas production. It was reported that the TFB reactor are efficient to facilitate gas-liquid mass transfer during production of methane (CH4) from carbon dioxide (CO2) and hydrogen (H2). The exogenous H2 injection in in-situ biogas upgrading decreased CO2 content from 51.35% to 16.72% and upgrade CH4 content from 48.65% to 81% in the output gas. The reactor CH4 production rate reached 0.89 L/LR•d and the H2 utilization efficiency of 98% was accomplished. Furthermore, the results showed that chemical oxygen demand removal efficiency of digestate reached to a maximum of 64% in 10 days hydraulic retention time. The microbial analysis indicated hydrogenotrophic Methanobacterium ferruginis was highly abundant in the liquid and biofilm phase, while acetoclastic Methanosarcina flavescens localized in the biofilm phase. The findings from this work showed that digestate can be simultaneously exploited for improving effluent quality and biogas upgrading.

Performance evaluation of desludged and upgraded waste stabilisation ponds: A case study, Botswana

The scarcity of fresh water for agricultural purposes requires the reuse of wastewater, if the effluent is of acceptable quality and is regularly monitored. The quality of the wastewater in the individual treatment units of waste stabilisation ponds was monitored after desludging and upgrading with a trickling filter unit. The overall hydraulic retention time had increased to 80% of the design value compared to 30% before desludging and upgrading. The biochemical oxygen demand, the chemical oxygen demand, the turbidity, and total suspended solids effluent concentrations were 41 ± 8 mgL−1, 83 ± 9.3 mgL−1, 43 ± 37 NTU, and 45 ± 38 mgL−1 respectively, compared to 40 mgL−1, 190 mgL−1, 145 ± 66 NTU, and 150 ± 127 mgL−1 before desludging and upgrading.The corresponding national thresholds for biochemical oxygen demand, turbidity and total suspended solids are 30, mgL−1, 30 NTU, and 25 mgL−1 respectively. Effluent log counts after upgrading were 2.4 ± 2.32 2.96 ± 2.3, 2.82 ± 2.42, and 2.44 ± 2.37 respectively, for E. coli, and the total coliforms and faecal coliforms compared to 5.4 ± 4.1, 5.1 ± 4.1, and 4.1 ± 23 log counts before upgrading. Helminth eggs were greater than 1 egg L−1 in the final effluent. The pHosphate effluent concentration was greater than the national threshold value (1.5 mgL−1) for discharge into the environment. Desludging and the addition of the trickling filter improved the removal efficiency of some of the contaminants. Operation and maintenance of the system needs to be improved and monitored to find out insights into poor performance even after desludging and addition of a trickling filter unit.

Simulated Modelling, Design, and Performance Evaluation of a Pilot-Scale Trickling Filter System for Removal of Carbonaceous Pollutants from Domestic Wastewater

The aim of the present study is to assess the wastewater treatment efficiency of a low-cost pilot-scale trickling filter (TF) system under a prevailing temperature range of 12 °C–38 °C. Operational data (both influent and effluent) for 330 days were collected from the pilot-scale TF for various physicochemical and biological parameters. Average percentage reductions were observed in the ranges of 52–72, 51–73, 61–81, and 74–89% for BOD5, COD, TDS, and TSS, respectively, for the whole year except the winter season, where a 74–88% reduction was observed only for TSS, whilst BOD5, COD, and TDS demonstrated reductions in the ranges of 13–50, 13–49, and 23–61%, respectively. Furthermore, reductions of about 43–55% and 57–86% in fecal coliform count were observed after the 1st and 6th day of treatment, respectively, throughout study period. Moreover, the pilot-scale TF model was based on zero-order kinetics calibrated at 20 °C using experimental BOD5 data obtained in the month of October to calculate the k20 value, which was further validated to determine the kt value for each BOD5 experimental setup. The model resulted in more accurate measurements of the pilot-scale TF and could help to improve its ability to handle different types of wastewater in the future.

Assessment of removal efficiency of pharmaceutical products from wastewater in sewage treatment plants: A case of the sewerage systems Ghana limited, Accra

Pharmaceuticals put the environment at high risk when found in products of wastewater treatment plants, hence need to be removed efficiently. This study quantified selected pharmaceutically active compounds (PhACs) (diclofenac, aspirin, paracetamol, and ibuprofen) in wastewater and evaluated its removal efficiency from wastewater treatment plant (WWTP). Samples were taken from the WWTP of the Sewerage Systems Ghana Limited (SSGL) for 18 consecutive days. Both effluents and influents were tested in the laboratory to determine the concentrations of the various pharmaceutical products. The results reveal diclofenac as the PhAC with the highest concentration in the influent with an average of 121.31 μg/ml. Paracetamol recorded an average of 65.54 μg/ml, then ibuprofen with an average of 19.54 μg/ml. Aspirin was the PhAC with the lowest concentration in the influent with an average of 0.27 μg/ml. Further assessment was also done on the trickling filter (biological filter) which is part of the process plant at the secondary stage to assess how the trickling filter aids in the removal of these selected pharmaceuticals.The average removal efficiency found were; diclofenac 74%, aspirin 93%, paracetamol 98%, and ibuprofen 99%. The technologies suggested for improvement, particularly for diclofenac, based on comprehensive literature were phototransformation and sorption of diclofenac onto sludge which occurs via absorption and adsorption, that can be adopted by the management of the WWTP at SSGL to help increase the removal efficiency of the selected PhACs. It was also identified that the trickling filter is the stage that substantially aids in the removal of the selected pharmaceuticals due to its special features.

Overview of Biological Treatment Technologies for Greywater Reuse

Greywater is a wastewater discharge originating from kitchen sinks, showers, baths, washing machines and dishwashers. Properly treated greywater can be recycled to meet global water shortages that is expected to affect 2.7 billion people around the world by 2025. Global water shortage can result in a reduction in agricultural land and increased dissertation leading to poverty, faming, war, illegal migration and human trafficking. Greywater contains fewer pathogens than domestic wastewater, is generally safer to handle and easier to treat and reuse onsite for toilet flushing, landscape and crop irrigation. Recycling of grey water provides substantial benefits for both the water supply system by reducing the demand for fresh clean water, and for the wastewater system by reducing the amount of wastewater required to be conveyed and disposed of. In this paper, the existing biological treatment systems for greywater are reviewed. These are: (a) constructed wet land, (b) sequencing batch reactor, (c) vertical flow bioreactor, (d) membrane bioreactor, (e) up-flow anaerobic sludge blanket, (f) rotating biological contractors, (g) trickling filters, (h) aerated lagoons, (i) anaerobic up-flow filter, and (j) expanded bed up-floe reactor. In a biological treatment, the degradation and transformation of greywater constituents are facilitated by the biochemical reactions carried out by microorganisms in the liquid medium. However, the effluent of biologically treated greywater may contain pathogenic microorganisms, requiring a final disinfection step to eliminate the risk of contracting pathogenic diseases. Selection criteria for a disinfectant include: (a) non-toxicity to humans, domesticated animals, and aquatic ecosystems, (b) low cost (c) easy handling, (d) reliable analysis, and (e) a satisfactory residual concentration. Any disinfection process selected (whether chemical oxidants or irradiation treatment is selected) should be evaluated taken into consideration the conditions of the wastewater source and existing biological treatment design.

Clarification of Biologically Treated Wastewater in a Clarifier with Suspended Sludge Layer

The article presents the results of an experimental study on the clarification of biologically treated wastewater in a clarifier with a suspended sludge layer. The pilot plant was receiving effluent from trickling filters treating municipal wastewater. An experimental clarifier worked under steady-state conditions considering the influent characteristics and variable operating parameters in terms of flow velocities and height of the suspended layer. From the experimental dependences between different technological parameters it was found that the optimum range of the upward flow velocities providing a dynamic equilibrium of the suspended layer was 0.6–1.4 mm/s. Upward flow velocities below 0.5 mm/s can lead to sludge compaction at the bottom of the unit, while values greater than 1.8 mm/s may cause sludge washout. It was also found that higher suspended layer height values favor higher efficiency of the clarifier and can achieve suspended solids in the discharge of less than 5.0 mg/L; this height should be greater than 0.6 m Technological efficiency of the experimental clarifier was significantly higher than the conventional unit and was comparable with tertiary treatment technologies.

Recirculation in Trickling Filters. (Dept. C)

Recirculation is the least understood of factors that affect on the mechanism and performance of the trickling filter. When recirculation is used, this works out in to applying almost the same organic mass to the trickling filter but with the increased hydraulic rate and a lower organic concentration than without recirculation. In this analysis, the organic concentration was divided into low organic concentration where the first order kinetic prevails and high organic concentration where the zero order kinetic predominates. The effect of recirculation on trickling filter performance under the two kinetic conditions were studied theoretically and by manipulating other researchers data found in the literature. The effect of recirculation on the trickling filter performance using design models was also investigated.

Analyses of deodorization performance of mixotrophic biotrickling filter reactor using different industrial and agricultural wastes as packing material

In this study, to efficiently remove malodorous gas and reduce secondary pollution under mixotrophic conditions, pine bark, coal cinder, straw and mobile bed biofilm reactor (MBBR) fillers were used as packing materials in a biological trickling filter (BTF) to simultaneously treat high-concentration H2S and NH3. The results showed that the removal rate of BTF-A filled with pine bark was the highest, which was 86.31% and 94.06% under the H2S and NH3 loading rates of 53.59 g/m³·h while the empty bed residence time (EBRT) was 40.5 s. The theoretical maximum load was obtained by fitting the kinetic curve, and the value were 90.09 g H2S m-³·h−1 and 172.41 g NH3 m-³·h−1. Meanwhile, after treating with 720 ppm of NH3, the average concentration of NO3- in the BTF circulating fluid was only 127.58 mg/L, indicating the better performance of secondary pollutants control. Microbiological analysis showed that Dokdonella, Micropruina, Candidatus_Alysiosphaera, Nakamurella and Thiobacillus possessed high abundance at the genus level, and their entire percentage in four BTF reactors were 62.87%, 46.32%, 47.98%, and 57.35% respectively. It is worthwhile that the genera Comamonas and Trichococcus with heterotrophic nitrification and aerobic denitrification capabilities and proportion of 3.66%, 1.45%, 5.43%, and 3.23% were observed in four reactors.

Effects of Seasonal Variation on Performance of Conventional Wastewater Treatment System

The study was to determine the seasonal differences of conventional wastewater treatment process. This was done by sampling and analyses of wastewater samples from four different points during the dry and wet seasons of the year 2019. Water samples were taken from influent point, primary effluent, trickling filter effluent and final effluent. Gravimetric method was used in determining Total Suspended Solids (TSS) and Total Dissolved Solids (TDS). The BOD 5 technique was used for determination of Biological Oxygen Demand (BOD) and the digestion method was used for determination Chemical Oxygen Demand (COD). Temperature, pH and conductivity were measured using respective meters. Analysis of Variance showed that there was significant difference (p < 0.05) in all the parameters quantified at all the points of treatment during the two seasons. The results showed that BOD and COD both reduced from one point to the next during the two seasons of study. The TSS levels increased after primary pond effluent undergoing treatment at the trickling filter and the temperature also increased after the trickling filter effluent undergoing treatment at oxidation ponds. The levels of conductivity and TDS decreased from one treatment stage to the next during dry season but during the wet season the levels of these parameters increased from one stage to the next except that the levels reduced after the primary pond effluent underwent treatment at the trickling filter. The various stages of wastewater treatment plant under were effective during the two seasons however, wet season recorded lower figures for most of the parameters. Keywords: effluent, influent, wastewater, seasonal variation, ponds DOI: 10.7176/JEES/11-7-06 Publication date: July 31 st 2021

An integrated assessment of environmental, economic, social and technological parameters of source separated and conventional sanitation concepts: A contribution to sustainability analysis

Resource recovery and reuse from domestic wastewater has become an important subject for the current development of sanitation technologies and infrastructures. Different technologies are available and combined into sanitation concepts, with different performances. This study provides a methodological approach to evaluate the sustainability of these sanitation concepts with focus on resource recovery and reuse. St. Eustatius, a small tropical island in the Caribbean, was used as a case study for the evaluation. Three source separation-community-on-site and two combined sewerage island-scale concepts were selected and compared in terms of environmental (net energy use, nutrient recovery/reuse, BOD/COD, pathogens, and GHG emission, land use), economic (CAPEX and OPEX), social cultural (acceptance, required competences and education), and technological (flexibility/adaptability, reliability/continuity of service) indicators. The best performing concept, is the application of Upflow Anaerobic Sludge Bed (UASB) and Trickling Filter (TF) at island level for combined domestic wastewater treatment with subsequent reuse in agriculture. Its overall average normalised score across the four categories (i.e., average of average per category) is about 15% (0.85) higher than the values of the remaining systems and with a score of 0.73 (conventional activated sludge – centralised level), 0.77 (UASB-septic tank (ST)), 0.76 (UASB-TF - community level), and 0.75 (ST - household level). The higher score of the UASB-TF at community level is mainly due to much better performance in the environmental and economic categories. In conclusion, the case study provides a methodological approach that can support urban planning and decision-making in selecting more sustainable sanitation concepts, allowing resource recovery and reuse in small island context or in other contexts.

Pharmaceuticals and environmental risk assessment in municipal wastewater treatment plants and rivers from Peru

This is the first study dealing with removal of the pharmaceutical substances in municipal wastewater treatment plants (MWWTPs) from Peru and the impact of these compounds in surface waters receiving treated wastewater. To this aim, samples from MWWTP of Lima (Peruvian Coast), MWWTP of Cusco, Puno and Juliaca (Peruvian Highlands), as well surface water (confluence of Torococha and Coata rivers in Juliaca) were analyzed. A total of 38 target pharmaceuticals were included in this study and were determined by Liquid Chromatography coupled to tandem Mass Spectrometry (LC-MS/MS). Around 60% and 75% of the target pharmaceuticals could be quantified in surface water and MWWTPs, respectively. Acetaminophen was the drug found at the highest concentration, and it was present in all the treated wastewater samples reaching average values above 100 μg/L in the department of Puno. The gabapentin anti-epileptic drug (up to 11.85 μg/L in MWWTP Lima) and the antibiotics clarithromycin, trimethoprim, ciprofloxacin, sulfamethoxazole and azithromycin (1.86 to 4.47 μg/L in MWWTP Lima) were also found at moderate concentrations in the treated wastewater. In surface water, the highest concentration corresponded also to acetaminophen (28.70 μg/L) followed by sulfamethoxazole (4.36 μg/L). As regards the pharmaceuticals removal, data of this work showed that the MWWTP Cusco (aerobic biologic process by synthetic trickling filters as secondary treatment) was more efficient than the MWWTP Lima (a preliminary treatment that combines grilles, sand trap, degreaser-aerated and sieved of 1.0 mm). However, many pharmaceuticals (around 50% of the compounds investigated) presented concentrations in treated wastewater similar or even higher than in influent wastewater. The environmental ecological risk of pharmaceuticals was assessed based on calculated Risk Quotient (RQ) in the treated wastewater and surface water from the concentration data found in the samples. According to our data, three antibiotics (clarithromycin, ciprofloxacin, clindamycin) and the analgesic acetaminophen posed high environmental risk (RQ ≥ 1) on the aquatic environment. In the river, all antibiotics (except norfloxacin) as well as the analgesic-anti-inflammatory compounds acetaminophen, diclofenac posed a high environmental risk (RQ ≥ 1). Based on data reported in this work for the first time in water samples from Peru, it can be deduced that the treatment processes applied in important cities from Peru are not enough efficient to remove pharmaceuticals in wastewater. As a consequence, severe environmental risks associated to the presence of pharmaceuticals in treated wastewater and surface water are expected; so complementary treatment processes should be implemented in the MWWTPs for a more efficient elimination of these compounds.

Effects of Packing Media and the Insertion of Vegetation on the Performance of Biological Trickling Filters

The use of the plant Chrysopogon zizanioides (vetiver), able to develop under adverse conditions while removing a great number of pollutants, in constructed wetlands (CWs) is widely reported. Regarding the biological trickling filters (BTFs), the selection of the media is one of the most important factors in its performance. We investigated whether the addition of vegetation improves the efficiency of the basic parameters of BTFs with gravel. In addition, due to the properties of light expanded clay aggregate (LECA), we evaluated whether the support media composed of vetiver and LECA is able to increase the media’s oxygenation. The efficiencies were 39, 49, 56, and 49% for biochemical oxygen demand (BOD) and 27, 20, 12, and 31%, for total Kjeldahl nitrogen (TKN) in BTFLV (vetiver with LECA), BTFL (LECA only), BTFGV (vetiver with gravel) and BTFG (gravel only), respectively. LECA when associated with vetiver may have provided higher aeration of the filter, denoted by the higher nitrate effluent concentration (0.35, against 0.03, 0.06, and 0.10 mg L−1 for BTFL, BTFGV, and BTFG). Vetiver had no improvement on BTFs performance concerning BOD. However, associated with LECA, its use could be viable to remove dissolved forms of nitrogen.

Modeling-based performance evaluation of novel cascade cum trickling filter wastewater treatment system

Modeling-based performance evaluation of novel cascade cum trickling filter wastewater treatment system

Ultra-low energy consumption process (PN+Anammox) for enhanced nitrogen removal from decentralized sewage

An ultra-low energy consumption continuous flow (UECF) process was used for enhanced nitrogen removal from rural sewage. The ammonia in sewage was first oxidized to nitrite in a bio trickling filter (BTFPN) supplemented with natural oxygen. A stable nitrite accumulation ratio (NAR) of 93.2% was maintained by adding 5 mg/L NH2OH every seven days. BTFPN effluent was then combined with certain portion of rural sewage (1:1.2 to 1:1.5) and introduced to an upflow anaerobic sludge blanket reactor, where the nitrogen-containing pollutants were removed by Anammox process (UASBAMX). Effluent total nitrogen (TN) of 6.7 mg/L and a TN removal efficiency of 93.7% were obtained when influent chemical oxygen demand (COD), NH4+-N and TN were 321.9, 74.2 and 82.7 mg/L, respectively. Advanced nitrogen removal, based on the desirable cooperation between Anammox bacteria (Ca. Brocadia, 2.3%) and partial denitrification bacteria (Thauera, 4.2%), was achieved over 300 days of stable operation. Considering the nitrogen balance, 57.9% of nitrate generated in Anammox was reduced to nitrite by partial denitrification, and Anammox contributed 88.1% of nitrogen removal and 7.6% of denitrification. Compared with conventional nitrification and denitrification processes, UECF requires no mechanical aeration, no external carbon, produces 76.6% less external sludge, and reduces CO2 emissions by 92.3%.

A Preliminary Study on the Use of Xylit as Filter Material for Domestic Wastewater Treatment

The aim of the study was to verify two morphological forms (“angel hair” and “scraps”) of xylit as a trickling filter material. The study was carried out on two types of polluted media: septic tank effluent (STE) and seminatural greywater (GW). The basic wastewater quality indicators, namely, chemical oxygen demand (COD), biochemical oxygen demand (BOD5), total suspended solids (TSS), ammonium nitrogen (NNH4), and total phosphorus (Ptot) were used as the indicators of treatment efficiency. Filtering columns filled with the investigated material acted as conventional trickling filters at a hydraulic load of 376–472 cm3/d during the preliminary stage, 198–245 cm3/d during stage I, and 184–223 cm3/d during stage II. The removal efficiency of the two morphological forms of xylit did not differ significantly. The average efficiencies of treatment were as follows: for COD, over 70, 80, and 85% for preliminary stage, stage I and stage II, respectively; for BOD5, 77–79% (preliminary stage); for TSS, 42% and 70% during the preliminary stage, and 88, 91, and 65% during stage I; for NNH4, 97–99% for stage I and 36–49% for stage II; for Ptot, 51–54% for stage I and 52–56% for stage II. The study demonstrated that xylit was a material highly effective in wastewater quality indicators removal, even during the initial period of its use.

Inorganic carbon limitation during nitrogen conversions in sponge-bed trickling filters for mainstream treatment of anaerobic effluent

Anaerobic sewage treatment is a proven technology in warm climate regions, and sponge-bed trickling filters (SBTFs) are an important post-treatment technology to remove residual organic carbon and nitrogen. Even though SBTFs can achieve a reasonably good effluent quality, further process optimization is hampered by a lack of mechanistic understanding of the factors influencing nitrogen removal, notably when it comes to mainstream anaerobically treated sewage. In this study, the factors that control the performance of SBTFs following anaerobic (i.e., UASB) reactors for sewage treatment were investigated. A demo-scale SBTF fed with anaerobically pre-treated sewage was monitored for 300 days, showing a median nitrification efficiency of 79% and a median total nitrogen removal efficiency of 26%. Heterotrophic denitrification was limited by the low organic carbon content of the anaerobic effluent. It was demonstrated that nitrification was impaired by a lack of inorganic carbon rather than by alkalinity limitation. To properly describe inorganic carbon limitation in models, bicarbonate was added as a state variable and sigmoidal kinetics were applied. The resulting model was able to capture the overall long-term experimental behaviour. There was no nitrite accumulation, which indicated that nitrite oxidizing bacteria were little or less affected by the inorganic carbon limitation. Overall, this study indicated the vital role of influent characteristics and operating conditions concerning nitrogen conversions in SBTFs treating anaerobic effluent, thus facilitating further process optimization.

Reactors and active biomass potential as inoculum for nitrogen removal

The potential of three different kind of reactors and active biomass to be used as inoculum for nitrogen removal was verified. Sludge samples were collected from a Membrane Bioreactor (MBR), a previous tank of a Moving Bed Biofilm Reactor (MBBR) and a Trickling Filter (TF). Samples were compared according to bacterial activity in batch tests and their microbiology (16 s rRNA sequences). The microorganisms examined were: AOB, NOB, anammox bacteria and OHO. Results showed that the richest sample was from MBR (Chao value equals 581). However, the bacterial activity was greater in MBBR sample (qAOO,NH4 equals 0.002 mgN·mgVSS−1·h−1; qNOO,NO2_NO3 equals 0.001 mgN·mgVSS−1·h−1 and qNOX_N2,SB equals 10.0 mgN·mgVSS−1·h−1). Therefore, MBBR WWTP was shown to have the best inoculum and operating conditions for nitrogen conversion and removal. Besides, if aeration is provided as low as necessary for AOB to start the activity in denitrification tank, simultaneous partial nitrification, and denitrification (SPND) can occur.