Optimum Hydraulic Retention Time Research Articles

Maximization of bio-hydrogen production from winery vinasses using on-line feedback control

Continuous biohydrogen production by dark fermentation valorizes organic effluents like winery vinasse (WV), being an economical alternative to fossil fuels, to produce clean and renewable hydrogen. Trickling bed reactors (TBR) operated with low hydraulic retention time (HRT) favor hydrogen production. However, its large-scale application has still been limited in the literature due to possible operational risks and costs. To maximize the hydrogen production rate (HPR) rapidly, an innovative on-line feedback control was evaluated using WV in a TBR. Based on continuous HPR measurements, the strategy alternates the operation between a high HRT of 5.5 h and a low HRT of 3 h (an organic shock load) by detecting either a peaking phenomenon during the transient or the steady state after it. Use of the controller increased the mean HPR to 177.5 ± 12.3 mLH2⋅Lreac−1⋅h−1 from 93.9 ± 9.9 mLH2⋅Lreac−1⋅h−1 under a usual fixed HRT operation, and only 91.5 h were needed to automatically find the optimal mean HRT at 3.76 ± 0.15 h. Bacterial community and metabolite analysis helped explain the increase in hydrogen yield (1.1 ± 0.4 mmol H2gCODadded−1) by a cross-feeding interaction between lactic acid and hydrogen-producing bacteria.

Photo-fermentative hydrogen production from cheese whey: Engineering of a mixed culture process in a semi-continuous, tubular photo-bioreactor

This work approaches the engineering of photo fermentative hydrogen production from cheese whey, for the scale-up of photo-bioreactors. Firstly, a brief review has been performed to identify the optimal reactor configuration as well as the main literature lacks. Results of the review analysis suggest that tubular photobioreactors are effective for the photo fermentation process. On the other hand, one of the main drawbacks to the scale-up of the proposed systems is the wide use of pure cultures, which requires aseptic environments and carefully controlled conditions. Based on the critical evaluation of the state of the art, a semi-continuous tubular photobioreactor, performing mixed culture hydrogen production from cheese whey, under unsterile conditions, was started up. Due to the lack of studies in this field, the case study was developed to provide a methodology for the reactor start-up, which represents the most critical phase of its operation. Preliminary tests were performed to choose the optimal operating conditions. To assess the effectiveness of cheese whey, results were compared to those obtained from a glucose based synthetic substrate, under steady state conditions. Experimental outcomes showed that the optimal Hydraulic Retention Time was 2 days and the most appropriate recirculation/pumping system consisted of an intermittent peristaltic pump. The semi-continuous feeding of cheese whey resulted in 87 mL/L d of hydrogen, which was similar to the productivity obtained under glucose feeding. The characterization of the residual organic content further indicated the possible accumulation of polyhydroxyalcanohates, which was estimated to constitute about the 40% of the total residual COD. These results further addressed the identification of key points to be better investigated to promote the effective photo fermentation scale-up for cheese whey valorization, such as the enhancement of the illumination conditions as well as the search for strategies to improve the uniform exposure of microbial cells to light.

A2O–MBR–BAF–O3 process for treating high organic wastewater with high ammonia nitrogen

In recent years, many WWTPs in China need to be upgraded and reconstructed due to the emission standards improvement. The WWTP influent is complex in composition and contains many hard-to-degrade organic matter. The indices (e.g., chroma, chemical oxygen demand (COD), ammonia nitrogen (NH4+–N), total nitrogen (TN), and suspended substance) are relatively high. In this paper, the anaerobic–anoxic–oxic (A2O)–membrane bioreactor (MBR)–biological aerated filter (BAF)–O3 process was proposed for the first time. The practical process was used to degrade COD and NH4+–N, TN, and chroma simultaneously. Under the adjusted optimal hydraulic retention time (12.5 h), internal reflux ratio of the intermixture (200 %), and O3 contact time (15 min), the removal efficiencies of COD, NH4+–N, TN, total organic carbon, UV254, and chroma were 94.50 %, 99.13 %, 78.21 %, 95.18 %, 90.60 %, and 78.66 %, respectively. The effluent quality satisfied the first grade A criteria (GB 18918–2002) in China. The ultraviolet-visible and excitation-emission-matrix spectra of water samples during the O3 oxidation were analyzed. It showed that the reaction was effective in removing chroma and hard-to-degrade organic matter that could not be treated by the previous process, and humic acids that was the main fluorescent organic matter in the wastewater.

Metagenomic analysis of microbial community and metabolic pathway of simultaneous sulfide and nitrite removal process exposed to divergent hydraulic retention times

The role of hydraulic retention time (HRT) on S0 production was assessed through metagenomics analyses. Considering comprehensive performance for the tested HRTs (0.25–13.33 h), the optimal HRT was 1 h, while respective sulfide and nitrite loading rate could reach 6.84 kg S/(m3·d) and 1.95 kg N/(m3·d), and total S0 yield was 0.36 kg S/(kg (VSS)·d). Bacterial community richness decreased along the shortening of HRT. Microbacterium, Sulfurimonas, Sulfurovum, Paracoccus and Thauera were highly abundant bacteria. During sulfur metabolism, high expression of sqr gene was the main reason of maintaining high desulfurization load, while lacking soxB caused the continuous increase of S0. Regarding nitrogen metabolism, the rapid decrease of nitrite transporter prevented nitrite to enter in cells, which caused a rapid decrease of nitrite removal under extreme HRT. Adjusting HRT is an effective way to enhance S0 production for the application of the simultaneous sulfide and nitrite removal process.

Ammonium recovery from agro-industrial digestate using bioelectrochemical systems.

Growing food and biomass production at the global scale has determined a corresponding increase in the demand for and use of nutrients. In this study, the possibility of recovering nitrogen from agro-industrial digestate using bioelectrochemical systems was investigated: two microbial electrolysis cells (MECs) were fed with synthetic and real digestate (2.5 gNH4+-N L-1). Carbon felt and granular graphite were used as anodes in MEC-1 and MEC-2, respectively. As to synthetic wastewater, the optimal nitrogen load (NL) for MEC-1 and -2 was 1.25 and 0.75 gNH4+-N d-1, respectively. MEC-1 showed better performance in terms of NH4+-N removal efficiency (39 ± 2.5%) and recovery rate (up to 70 gNH4+-N m-2d-1), compared to MEC-2 (33 ± 4.7% and up to 30 gN m-2d-1, respectively). At the optimal hydraulic retention time, lower NH4+-N removal efficiencies and recovery rates were observed when real digestate was fed to MEC-1 (29 ± 6.6% and 60 ± 13 gNH4+-N m-2d-1, respectively) and MEC-2 (21 ± 7.9% and 10 ± 3.6 gNH4+-N m-2d-1, respectively), likely due to the higher complexity of the influent. The average energy requirements were 3.6-3.7 kWh kgNremoved-1, comparable with values previously reported in the literature and lower than conventional ammonia recovery processes. Results are promising and may reduce the need for costly and polluting processes for nitrogen synthesis.

Removal of Pathogens from Domestic Wastewater Using Small‐Scale Gradual Hydroponics Planted with Duranta erecta, Addis Ababa, Ethiopia

This study aimed to evaluate the treatment potential of gradual hydroponics planted with Duranta erecta in the removal of pathogens from domestic wastewater. Two experimental and control units were configured in series. Each unit contains three bioreactors and was arranged in a cascaded configuration. The two experimental units used both plant and media, but the two control units used only media to treat the wastewater. Gravel and polyester sponge were used as media. Experimental unit 1 and control unit 1 used gravel as media; however, experimental unit 2 and control unit 2 used polyester sponges as media. The experiment was operated at hydraulic retention times of 1, 3, 5, and 7 days in a continuous mode. The performance of the hydroponic system was evaluated by characterizing the influent and effluent quality using standard methods. At optimum hydraulic retention time (7 days), the average removal of experimental units 1 and 2 was 98.7% and 89.8% for heterotrophic bacteria, 96.2% and 86.8% for total coliform, and 92.9% and 84.0% for fecal coliform, respectively. Analysis of variance showed that there was a significant difference (P < 0.05) between the two experimental and control units in removing pathogens, but no significant difference (P > 0.05) was observed between the two experimental units and between the two control units. Heterotrophic bacteria and coliforms were satisfactorily removed from domestic wastewater via a gradual hydroponic system. Hence, the hydroponic treatment system planted with Duranta erecta has a promising potential in the removal of pathogens from domestic wastewater in developing countries including Ethiopia.

Advanced biokinetic and hydrodynamic modelling to support and optimize the design of full-scale high rate algal ponds

High rate algal ponds (HRAP) are known for their suitability to treat wastewater and to produce microalgal biomass, which can be converted into bioproducts. However, full-scale application of HRAP is still limited to few cases, and design procedures are not consolidated or standardized. In this study, a demonstrative-scale HRAP system for secondary wastewater treatment to be implemented in India (treatment capacity of 50 m3·d−1) has been designed combining conventional dimensioning techniques and advanced modelling tools. The objective of the study was to assist, verify and optimize the conventional dimensioning of the secondary HRAP by means of simulations predicting the behaviour of the system in the specific local conditions under different configurations and operational strategies. Biokinetic modelling and hydrodynamic analysis using Computational Fluid Dynamics (CFD) were carried out. The simulations performed with the biokinetic model showed that the optimal hydraulic retention time to enhance nutrient removal and biomass production is 4 days. For the hydrodynamic modelling, a 3D model of the HRAP was built to simulate the hydrodynamic behaviour of 36 different designs. Simulations allowed quantifying the presence of low velocity zones as well as the land use efficiency of the different designs in terms of the useful area vs. the total occupied area. Two baffles and tear-shapes with a diameter equal to ¼ of the channel width was the most efficient configuration. Moreover, a technical–economic assessment of the system was carried out, resulting in an investment cost of 483 € per population equivalent and an operational cost of 0.19 € per m3 of treated wastewater.

Potential and characteristics of bio-H2 production from brewery wastewater by a maltose-preferring butyrate-type producer: Investigation in batch and semi-continuous cultures

In the context of "Peak CO2 emissions & Carbon neutrality", H2 energy, as the green and clean energy, will make an important contribution to the carbon emission reduction and carbon neutralization. Bio-H2 production from organic wastewater achieved not only pollutants removal, but also the H2 energy recovery and carbon emission reduction. In this study, a maltose-preferring producer of Clostridium butyricum NH-02 was investigated for the potential and performance of bio-H2 production from brewery wastewater in batch and semi-continuous fermentation. Appropriate initial pH 7.0 and organic loading of 21,173mg/L chemical oxygen demand (COD) (2670mg/L reducing sugar (RS)) stimulated the batch H2 fermentation efficiency with a maximum H2 yield of 1.89mol-H2/mol-RS and cumulative H2 production of 479.3mL/L. Comparing to the batch fermentation, semi-continuous fermentation showed significant improvement in H2 productivity and yield. The maximum cumulative H2 yield of 5.21mol-H2/mol-RS and production of 254.78mL were obtained with the optimal hydraulic retention time (HRT) at 47h after a 120h fermentation. This study demonstrated the potential of H2 production from brewery wastewater with C. butyricum, and a great improvement in H2 production in semi-continuous fermentation.

A radial basis function neural network based multi-objective optimization for simultaneously enhanced nitrogen and phosphorus removal in a full-scale integrated surface flow treatment wetland–pond system

In this study, a radial basis function neural network (RBFNN) model was developed and implemented in a multi-objective optimization procedure to determine the optimal hydraulic loading rate (HLR), hydraulic retention time (HRT), and mass loading rates (MLR) for enhanced removal of nitrogen and phosphorus by an integrated surface flow treatment wetland–pond system treating drinking source water in Yancheng, China. Prior to modelling, the system’s 6-year nitrogen and phosphorus removal efficiencies were found to trend downwards as effluent concentrations trended positively. Meanwhile, operating parameter interaction effects impacted final effluent quality. Thus, total nitrogen and total phosphorus removal were simulated by an RBFNN model with satisfactory R2 of 0.99 and 0.98 respectively. Optimal average HLR, HRT and MLR for 80% simultaneous removal efficiencies were subsequently determined to be 0.10860 ± 0.03 md-1, 30.43 ± 9.96 d and 306.416 ± 89.54 mgm-2d-1 respectively. The results highlight the feasibility of the RBFNN modelling based optimization procedure for treatment wetlands.

Possibilities of Obtaining Biogas from Manure and Amaranth

Introduction. The use of biomass allows increasing the rate of biogas formation and its specific yield. This work aims to study the kinetics of methanogenesis and determine the optimal duration of digestion and organic load, which are the main indicators of the technological process of biogas formation. Materials and Methods. The substrate (dairy manure, biomass of amaranth) was the study object. Experimental studies were carried out using a laboratory biogas plant. The computer program (certificate No. 2018662045) was used to obtain modified Gompertz models describing the kinetics of biogas formation. Based on the obtained data, the hydraulic retention time and organic loading rate (the key parameters in the design of biogas plants were determined). Results. The paper presents the experimental studies results of the biogas formation kinetics when using dry amaranth biomass. The Gompertz mathematical models were obtained. Methane-tank control parameters (hydraulic retention time and organic loading rate) were obtained for anaerobic digestion of a new substrate. Discussion and Conclusion. The use of new co-substrate Amaranthus retroflexus L. allowed increasing the specific biogas yield from dairy manure by 52.2 % and the ultrasonic pre-treatment in combination with the herbal supplement by 89.1 %. The optimal hydraulic retention time value was 10 days and organic loading rate was 4.1 kg of volatile solids per m3 of digester per day.

Effect of Hydraulic Residence Time on Removal Efficiency of Pollutants in Subsurface Flow Constructed Wetlands and Analysis of Denitrification Mechanism

This study used vertical and horizontal subsurface constructed wetlands with continuous inflow, to compare and analyze the effects of four hydraulic residence times on the removal efficiency of conventional pollutants. Using the optimal hydraulic retention time, the two types of wetlands were examined in terms of the stromal layer nitrification, denitrification, and ammonia oxidation abundance of functional genes, as well as the intensity of nitrification and denitrification. In addition, redundancy analysis and variance decomposition analysis were used to determine the main factors affecting nitrogen removal in the two kinds of wetlands, so that targeted improvement measures can be suggested. The best removal efficiency of conventional pollutants (COD, TP, TN, and NH4+-N) was achieved with a hydraulic retention time of 24 h, resulting in a removal rate of more than 70%. With a 24 h retention time, the removal rate of NH4+-N and TN and the intensity of nitrification and denitrification exhibited a gradually decreasing trend along the flow direction. Among the three functional genes, the abundance of denitrification functional genes (nirS) was much higher than that of nitrification functional genes (nxrA) and ammonia oxidation functional genes (AOB-amoA). In this study, the nitrogen removal ability of the two subsurface flow constructed wetlands was jointly affected by environmental factors and microbial factors, among which microbial factors contributed the most to nitrogen removal (55% and 48%). In addition, the removal rates of TN and NH4+-N were proportional to DO, specific surface area of substrate, COD concentration, as well as nitrification and denitrification functional genes, but inversely proportional to pH. Therefore, in order to improve the nitrogen removal efficiency of both systems, the amount of dissolved oxygen and carbon sources in the substrate layer should be increased, while the pH value should be appropriately reduced. Moreover, the horizontal subsurface constructed wetland significantly improves the nitrogen removal efficiency of the system, as the substrate layer has a larger specific surface area. This study provides a theoretical basis for the design of constructed wetlands and the selection of an optimal hydraulic residence time. Quantitative analysis of nitrogen removal pathways is of great significance for understanding the nitrogen removal mechanism and improving the nitrogen removal rate in constructed wetlands.

Using a sulfur autotrophic fluidized bed reactor for simultaneous perchlorate and nitrate removal from water: S disproportionation prediction and system optimization.

The sulfur autotrophic reduction (SAR) process is promising in co-reduction of perchlorate and nitrate from aqueous solution. To further understand the reaction process, we developed a sulfur autotrophic fluidized bed reactor where the proceeding extent of sulfur (S) disproportionation was predicted by Response surface methodology (RSM) for the first time. Three fundamental reaction parameters including the hydraulic retention time (HRT), co-existing nitrate concentration ([Formula: see text]) and recirculation ratio (R) were considered for reactor optimization. The results demonstrated that S disproportionation was promoted by long HRT and high R, whereas was inhibited by high [Formula: see text]. Also, the optimal HRT, [Formula: see text] and R were 0.50h, 10.00mg/L and 14, respectively, the bioreactor can achieve high reduction efficiency of perchlorate and nitrate (> 98.45%), and generate less sulfate (236.07mg/L). High-throughput sequencing showed that Chlorobaculum was related to S disproportionation, and Sulfurovum was associated with nitrate/perchlorate reducing. All results indicate that the sulfur autotrophic fluidized bed reactor is a promising candidate for the treatment of perchlorate and nitrate wastewater in future practical applications.

A kinetic study on the nitrification process in the upflow submerged biofilter reactor

ABSTRACT In extent of this study, ammonium removal from wastewater through biological nitrification process was performed in upflow biofilm reactors. The effects of hydraulic retention time (HRT) and nitrogen loading rate (NLR) on the nitrification process were investigated. For the nitrification process, the optimum HRT and NLR were determined to be 80 hr and 0.044 kg/m3.day, respectively. It is observed that the efficiency increased from 53% to 96% along with the increase in HRT from 22 hr to 80 hr and the decrease in NLR from 0.165 kg/m3.day to 0.044 kg/m3.day.The substrate consumption kinetics were studied in the attached growth reactor, and the Monod kinetic model, first-order kinetic model, modified Stover-Kincannon and Grau second-order kinetic models were examined. For the substrate consumption kinetic study, experimental studies were performed at 125, 150, 175, 200, 225 mg NH4-N/L substrate concentrations and 62 hr at HRT during the nitrification process. As a result of the considering kinetic studies, it was determined that the kinetic study was suitable for the modified Stover-Kincannon kinetic model that had the highest coefficient of regression by 0.997 and when the effluent NH4-N concentrations and NH4-N removal efficiencies calculated using kinetic models were examined, it was observed that the results closest to the experimental results (4.5, 10.1, 19.7, 26.2 and 42.3 mg NH4-N/L) were obtained through the modified Stover-Kincannon model (4.16, 10.71, 18.92, 28.12 and 39.51 mg NH4-N/L).

Nitrogen removal and bacterial mechanism in a hybrid anoxic/oxic baffled reactor affected by shortening HRT in treating manure-free piggery wastewater

A hybrid anoxic/oxic baffled reactor (HAOBR) with four compartments was constructed to treat manure-free piggery wastewater which was characterized by high ammonium (NH4+-N) and low chemical oxygen demand (COD) to total nitrogen (TN) ratio. To evaluate the suitable volumetric removal rate, hydraulic retention time (HRT) was decreased from 28 h to 16 h by stages, with the constant reflux ratio of 200% at 32 ± 1 °C. It was found that the optimal HRT is 20 h with the removal efficiency of COD, NH4+-N and TN in the steady phase averaging 79.1%, 99.5% and 93.2%, respectively. Meanwhile, the COD removed to TN removed ratio (CODrem/TNrem) averaged 0.94, indicating that anammox was the main approach to TN removal. Microbial community analysis further revealed that the main nitrogen removal pathway in the first two anaerobic compartments was heterotrophic denitrification, while autotrophic partial nitritation - anammox process dominated the last two aerobic compartments. This study presented a cost-effective bioprocess for treating organic wastewater with high NH4+-N and low COD/TN ratio.

Pilot-Scale Airlift Bioreactor with Function-Enhanced Microbes for the Reduction of Refinery Excess Sludge.

A pilot-scale airlift bioreactor (ALBR) system was built and operated continuously for refinery excess sludge (RES) reduction. Combined ALBR and function-enhanced microbes (composed of photosynthetic bacteria and yeast) were integrated into the system. The pilot-scale ALBR was operated for 62 days, and the start-up time was 7 d. Continuous operation showed that the sludge reduction efficiency was more than 56.22%, and the water quality of the effluent was satisfactory. This study focused on investigating the effects of hydraulic retention time (HRT) on the stability of the system and the effect of sludge reduction. Under different HRT conditions of 40, 26.7, 20, and 16 h, the sludge reduction rates reached 56.22%, 73.24%, 74.09%, and 69.64%, respectively. The removal rates of chemical oxygen demand (COD) and total nitrogen (TN) decreased with decreasing HRT, whereas the removal rate of NH4+-N increased. The removal rate of total phosphorus (TP) was approximately 30%. Results indicate that the ALBR and function-enhanced microbe system can reduce sludge and treat sewage simultaneously, and the effluent is up to the national emission standard. Addition of function-enhanced microbes can promote the degradation of petroleum hydrocarbon substances in the sludge, especially alkanes with low carbon numbers. This study suggests that the optimal HRT for the system is 16 h. The total operation cost of the ALBR combined with the function-enhanced microbe system can be reduced by 50% compared with the cost of direct treatment of the RES system.

The Tolerance of Anoxic-Oxic (A/O) Process for the Changing of Refractory Organics in Electroplating Wastewater: Performance, Optimization and Microbial Characteristics

In order to investigate the tolerance of an anoxic-oxic (A/O) process for the changing of refractory organics in electroplating wastewater, optimize the technological parameters, and reveal the microbial characteristics, a pilot-scale A/O process was carried out and the microbial community composition was analyzed by high-throughput sequencing. The results indicated that a better tolerance was achieved for sodium dodecyl benzene sulfonate, and the removal efficiencies of organic matter, ammonia nitrogen (NH4+-N), and total nitrogen (TN) were 82.87%, 66.47%, and 53.28% with the optimum hydraulic retention time (HRT), internal circulation and dissolved oxygen (DO) was 12 h, 200% and 2–3 mg/L, respectively. Additionally, high-throughput sequencing results demonstrated that Proteobacteria and Bacteroidetes were the dominant bacteria phylum, and the diversity of the microbial community in the stable-state period was richer than that in the start-up period.

Effect of hydraulic retention time on solid-phase denitrification reactor in recirculating aquaculture system

Hydraulic retention time (HRT) is one of the most critical operational parameters for solid-phase denitrification. The effect of HRT on solid-phase denitrification reactors (DR) packed with corrugated paperboard was investigated in recirculating aquaculture systems (RAS). Denitrification efficiencies of DR were 81.21–85.05% at HRTs of 0.5–2.0 h. The optimal HRT for denitrification was 2.0 h with a rate of 14.81 mg/(L substrate day). HRT significantly affected the bacterial community structure in DR by changing the population dynamics of the dominant bacteria and denitrifying functional bacteria such as Rhizobiaceae, Desulfovibrionaceae, and Arcobacteraceae. Moreover, the HRT of the DR showed a significant effect on the bacterial community in the nitrification reactor and culture water. Reducing HRT can promote the growth of total bacteria in the DR. However, it revealed a limiting effect on the abundance of key genes of the nitrogen cycle, including the amoA, nirK and nosZ. Under the condition of short HRT, the DR can also achieve a good denitrification effect, which provides feasible management measures for nitrogen removal in RAS.

Fate and removal of pentachlorophenol and diethylhexyl phthalate from textile industry wastewater by sequencing batch biofilm reactor: Effects of hydraulic and solid retention times

This study aimed to examine the effects of hydraulic retention time (HRT) and solid retention time (SRT) on the removal of diethylhexyl phthalate (DEHP) and pentachlorophenol (PCP) from real textile wastewater. Experiments were conducted daily and at different SRTs (10 d, 15 d, and 20 d) and HRTs (36 h, 48 h, and 60 h). The results showed that the optimal HRT and SRT for DEHP removal were 48 h and 20 d, respectively, and the removal efficiency reached 83.27%. Meanwhile, the highest removal efficiency was 75.5% for PCP at an HRT of 60 h and an SRT of 15 d. The addition of biocarriers to the reactor system was intended to facilitate microorganism growth and increase the average removal efficiencies of PCP and DEHP. Short HRTs and SRTs resulted in low micropollutant removal efficiencies. Based on the mass balance calculations, it was determined that biodegradation and sorption onto sludge were the main removal mechanisms for PCP and DEHP. The findings also revealed that using the optimal HRT and SRT is critical to achieve the highest growth of the bacteria responsible for the biodegradation of selected micropollutants. In the biocarrier amended system, biodegradation served and sorption onto sludge contributed to PCP removal. Conversely, the major removal mechanism for DEHP varied depending on the operating conditions. In particular, with increasing SRT, biodegradation became the dominant removal mechanism.

Study on the Decontamination Effect of Biochar-Constructed Wetland under Different Hydraulic Conditions

To explore the purification effect of biochar-constructed wetlands on rural domestic sewage, six types of biochar-constructed wetlands were constructed for experiments. Under different hydraulic conditions, the removal effects of each biochar-constructed wetland on chemical oxygen demand, ammonia nitrogen, total nitrogen, and total phosphorus in sewage were analyzed. The results showed that the removal rates of the four types of pollutants in each biochar-constructed wetland first increased and then decreased with the increase in hydraulic retention time, and the optimal hydraulic retention time range was 36–48 h. The highest removal rates of chemical oxygen demand, ammonia nitrogen, total nitrogen, and total phosphorus in the wetland were 97.34 ± 0.84%, 95.44 ± 1.29%, 98.95 ± 0.52%, and 97.78 ± 0.91%, respectively. The chemical oxygen demand (COD) removal rate of each biochar-constructed wetland increased first, then decreased with the increase in hydraulic load, and the optimal hydraulic load was 10 cm/d. The removal efficiency of ammonia nitrogen, total nitrogen, and total phosphorus of each biochar-constructed wetland gradually weakened with the increase in hydraulic load, and the optimal hydraulic load range was between 5 and 10 cm/d. Under these conditions, the highest removal rates of chemical oxygen demand, ammonia nitrogen, total nitrogen, and total phosphorus in the wetland were 92.15 ± 2.39%, 98.32 ± 0.48%, 96.69 ± 1.26%, and 92.62 ± 2.92%, respectively. Coconut shell and shell-constructed wetlands with the highest proportion of biochar in the matrix have the best removal effect on pollutants under different hydraulic conditions, and the wastewater purification effect is stronger, indicating that the addition of biochar is helpful for the removal of pollutants in constructed wetlands.

Techno-Economic Assessment of On-Farm Anaerobic Digestion System Using Attached-Biofilm Reactor in the Dairy Industry

In this study, a techno-economic assessment of an on-farm biogas system using an anaerobic biofilm reactor utilizing cow manure as a fermentation substrate was evaluated. A projection model was developed using Microsoft Excel software with three outputs, the size and dimension of a bioreactor, experimental microbial kinetic studies, and the economic studies based on the experimental results. Characterization analysis of cow manure wastewater showed the total solid (TS), total volatile solid (TVS), total carbohydrate (TC), chemical oxygen demand (COD), and pH values which were 10.95 g/L, 8.65 g/L, 6.65 g/L, 57.80 g/L, and 7, respectively. Using the modified Gompertz equation for the microbial studies, it was found that, at 37 °C and 20 days hydraulic retention time (HRT), the biogas yield was 934.54 mL/gVS, the volume of biogas produced was 11.28 m3/d, and 22.56 kWh of electricity was generated. The Gompertz prediction helps to determine the optimal HRT for the system so that the microorganisms are at their optimum stage to produce biogas. The economic analysis was done, and the results illustrated that, when the rate of cow manure produced was at 55 L/day.cow, the net present value (NPV) was RM 611,936.09, with a 13% internal rate of return (IRR), 0.14 return on investment (ROI), and 7.02 years of payback period (PP). By developing a techno-economic assessment that included all the necessary parameters such as sizing of the bioreactor, microbial kinetic studies, and economics of the plant, farmers could easily implement the system into their farms. This model showed that the anaerobic digestion system utilizing an attached biofilm with cow manure as a fermentation inoculum and substrate was applicable on an industrial scale to generate electricity and reutilize to the farm, at the same time generating additional income from the production of fertilizer.