Days Of Retention Time Research Articles

Design and development of a pilot plant for the treatment of pharmaceutical wastewater containing molasses

Abstract The present work deals with the anaerobic treatment of molasses-bearing pharmaceutical wastewater using a specifically designed downflow anaerobic bioreactor (DFAB). The capacity of the designed DFAB was 1,000 L of adequate volume with necessary operational controls. Two types of anaerobic treatment, i.e. mesophilic and thermophilic treatments, were applied to the anaerobic biotransformation of wastewater under investigation. The efficiency of both treatments was compared in terms of reducing biochemical oxygen demand (BOD) and chemical oxygen demand (COD) load, as well as methane production. The anaerobic digestion process was carried out with the help of bacterial strains. The bacterial strains used in the mesophilic operation were acclimatised and utilised for the thermophilic treatment, which is a cost-effective and sustainable approach. A significant reduction in BOD and COD content of the wastewater was noticed after 10 days of retention time. Nearly 72–83% and 80–90% reduction in BOD values were recorded under mesophilic and thermophilic operations, respectively. Approximately 73–86% and 82–93% of COD content were reduced by mesophilic and thermophilic treatment, correspondingly. Methane production of 67 and 74% was achieved under mesophilic and thermophilic treatment, respectively. The designed DFAB showed remarkable treatment efficiency for wastewater and methane production.

Hybrid constructed wetland for treatment of power plant effluent polluted with hydrocarbons

Constructed wetlands (CWs) have good potential for application in the treatment of various types of polluted water in Iraq, including industrial wastewater, due to their low cost relative to the current conventional treatment technologies. Hybrid CW with a continuous-flow system was tested for the treatment of highly polluted industrial wastewater from the Al-Najibiyia Power Plant in Basrah City for 72 days with 5 days of retention time. The system consisted of a horizontal subsurface flow system (HSSF) planted with Phragmites australis (Cav.) followed by a surface flow (SF) system planted with Hydrilla verticillata (L.f.) Royle. A second system without plants served as a contaminant control system. Total petroleum hydrocarbons (TPHs), petroleum aromatic hydrocarbons (PAHs) and water quality were measured for both raw and treated wastewaters and plant status parameters were monitored. The presence of both plants and substrate had a significant effect on the removal efficiency and mass removal rate of all pollutants at (p < 0.05). The planted system performance showed a percentage removal of pollutants reaching to: 65.9 % for BOD5, 91.0 % for COD and 88.8 % for total suspended solids (TSS) while removal efficiency of BOD5, COD and TSS for unplanted systems was only 44.7, 64.5 and 68.7 %, respectively. The removal efficiencies of TPHs, and PAHs by the hybrid system were 96.5, and 96.0 %, compared to only 71.0 % and 51.0 % for unplanted system, respectively, showing that hybrid CW could enhance pollutant removal efficiency better than single CW. It is revealed also that the high efficiency in removing pollutants is the result of the plant and substrate presence and the interaction between plants and the surrounding microbial community. Thus, constructed wetlands (CWs) are a good option for industrial wastewater treatment due to its simple construction and effectiveness to remove hydrocarbons.

Bioremediation of reverse osmosis concentrate generated from the treatment of landfill leachate.

The moisture content of municipal solid waste (MSW) and local precipitation events lead to the leachate generation from MSW landfills. The high concentration of organic pollutants in landfill leachate (LL) makes it hazardous, requiring treatment before disposal into the environment. LL is most commonly treated by reverse osmosis (RO), which generates large volumes of concentrate known as RO concentrate. This investigation aims to stabilize the RO concentrate through an inexpensive and effective bioremediation strategy. A bench-scale aerobic suspended growth reactor study was conducted using three commercial conversion agents, namely EM.1, Bokashi powder, and coir pith powder. Overall bench-scale efficiency of 63% was achieved in this study. The onsite studies were conducted in 7.5-m3 artificial ponds with 46% efficiency amid atmospheric influences and constraints. The overall efficiencies of both bench and field-scale studies were derived by ascertaining the arithmetic mean of the individual efficiency of the following parameters: chemical oxygen demand (COD), biochemical oxygen demand (BOD), and total dissolved solids (TDS). In contrast, the control pond with no conversion agents showed an increase in pollution concentration over the 100 days of retention time. The findings revealed that the investigated technology had a marginally lower evaporation rate and performed relatively well compared to traditional solar evaporation ponds. Moreover, the technology can be easily scaled-up and readily applied for RO concentrate treatment in MSW landfills.

Biogas yield using single and two stage anaerobic digestion: An experimental approach

Untreated sewage sludge is one of the biggest problems in India and around the globe. In the current study, we try to figure out an efficient technique that uses sewage sludge (SS) food waste (FW) to generate biogas. In this work, FW and SS are co-digested in single-stage anaerobic digestions (SSAD) and two-stage anaerobic digestions (TSAD) at various processing parameters, such as temperature, carbon-to-nitrogen (C/N) ratio, volatile solid (VS) percentage content, retention time (RT), and pH value. The high-solid digestion of FW and SS in the SSAD process reduces the biogas production rate compared to the TSAD process with 35 days of retention time at mesophilic temperature due to the oily substance from FW accumulating in the scum floating layer in the SSAD process. By altering the mass ratio between FW and SS (based on VS%), the TSAD process could be more effective. This ratio of 60:40 between FW and SS would produce more biogas with maximum efficiency in TSAD compared to the SSAD process. The results highlight an increase in biogas production and VS removal efficiency of the TSAD process 41.90% and 9.8%, respectively, compare to the SSAD process. The cumulative biogas yield in the TSAD process was 1914.8 ml and in the SSAD process was 1349.4 ml when the ratio of FW and SS was taken to be 60:40. In the TSAD process, Methane (CH4) concentrations increased on average from 51% to 75%, due to better substrate hydrolysis and more readily accessible volatile fatty acids in the second stage. The analysis shows the co-digestion approach and TSAD process might work together to overcome the limitations of the conventional SSAD procedure for FW or SS when used separately.

Fecal sludge treatment in a pilot-scale vertical-flow constructed wetland for the removal of helminth eggs

Abstract Eliminating parasites in fecal sludge (FS) remains one of the major concerns in developing countries. To address this issue, experiments were conducted in triplicate vertical-flow constructed wetland (VFCW) units corresponding to free flow, 7 days and 14 days of retention time (RT). The effect of plant density on the system's performance was monitored in each planted bed unit and compared to the non-planted unit (standard). Following a bi-monthly application rate of FS at a nominal load of 200 kg TS m−2 year−1, the performance of the system in terms of helminth egg removal was calculated for each hydraulic RT tested. Untreated FS applied on the bed units contained high parasitic egg loads with a median number of 62.51 helminth eggs/g. The removal efficiencies of helminth eggs ranged from 82 to 100% in the leachates and were affected by the hydraulic RTs and the presence of plants (p &amp;lt; 0.05). On the other hand, accumulated biosolids on the bed units still contained high concentrations of pathogens exceeding the WHO standards and should not be applied directly in agriculture.

The Application of Design of Experiments in the Hatchery Wastewater Treatment through Biological Method

This study was conducted to evaluate the most influential factors contributing to the removal of chemical oxygen demand (COD), nitrate-N, and total phosphorus in hatchery wastewater to optimize the removal process with the application of acclimatized mixed culture (AMC). The factors, namely, the ratio of AMC to synthetic wastewater (SW), support media, agitation speed, and retention times, were selected and were analyzed through two-level factorial analysis. The results suggested that the best conditions for maximum removal of each response was the ratio of 1 to 3 AMC: SW, absence of support media, 0 rpm agitation, and 4 days of retention time; where the removal values of COD, nitrate-N, and total phosphorus were 26.5%, 76.5%, and 42.9%, respectively. The two largest contributing factors obtained from the factorial analysis were analyzed by the Design-Expert software to determine the optimum conditions for waste removal through the central composite design of the Response Surface Methodology (RSM). The obtained removal values were up to 62%, 94%, and 46% for COD, nitrate-N, and phosphorus at each optimum condition. The results obtained were higher than those from factorial analysis for all responses. To sum up, the treatment of contaminated wastewater through biological treatment via acclimatized mixed culture can be applied. The optimum conditions determined from this study should bee helpful in scaling up the wastewater treatment process.

Application of response surface methodology for COD and ammonia removal from municipal wastewater treatment plant using acclimatized mixed culture

This study aimed to optimize conditions influencing the removal of chemical oxygen demand (COD) and ammonia-N in municipal wastewater by using acclimatized mixed culture (AMC). Two-level factorial analysis was used to investigate the factors affecting the degradation of COD and ammonia-N (%); ratio of synthetic wastewater (SW) to acclimatized mixed culture (AMC) (1:1 and 3:1), presence and absence of support media (Yes and No), agitation (0 rpm and 100 rpm) and hydraulic retention time (HRT) (2 and 5 days). A central composite design (CCD) under response surface methodology (RSM) determined the optimum agitation (0 rpm and 100 rpm) and retention time (2 and 5 days). The best conditions were at 3:1 of SW: AMC ratio, 100 rpm agitation, without support media, and 5 days retention time. COD and ammonia-N removal achieved until 57.23% and 43.20%, respectively. Optimization study showed the optimum conditions for COD and ammonia-N removal were obtained at 150 rpm agitation speed and 5 days of retention time, at 70.41% and 64.29% respectively. This study discovers the conditions that affect the COD and ammonia-N removal in the municipal wastewater using acclimatized mixed culture.

Photosynthetic upgrading of biogas from anaerobic digestion of mixed sludge in an outdoors algal-bacterial photobioreactor at pilot scale

Anaerobic digestion can biotransform the biodegradable fraction of sewage sludge into biogas, while the symbiotic action of algal-bacterial consortia can remove both the CO2 and H2S from biogas and nutrients from digestate. A 100 L anaerobic digester operated at 20 days of retention time coupled with a 180 L high-rate algal pond (HRAP) engineered to upgrade the biogas and treat the liquid fraction of the pilot digester was optimized along four operational stages: (I) operation with a greenhouse during winter; (II) operation without greenhouse; (III) process supplementation with NaHCO3; (IV) process supplementation with Na2CO3. The biogas produced was composed of 63.7 ± 2.9% CH4, 33.7 ± 1.9% CO2, 0.5 ± 0.3% O2 and 1.6 ± 1.1% N2. An average methane productivity of 324.7 ± 75.8 mL CH4 g VSin−1 and total COD removals of 48 ± 20% were recorded in the digester. The CH4 concentration in the biomethane gradually decreased to 87.6 ± 2.0% and 85.1 ± 1.3% at the end of stage I and II, respectively, attributed to the loss of inorganic carbon in the HRAP. The supplementation of NaHCO3 and Na2CO3 mediated an increase in the CH4 content to 90.4 ± 1.5 and 91.2 ± 0.7% in stages III and IV, respectively. Steady state CO2 removals of 90% and 88% in stages I and II, and 95.7 and 97.6% in stages III and IV, respectively, were recorded. A constant biomass productivity of 22 g m−2 d−1, set by daily harvesting 26.5 g dry algal-bacterial biomass from the bottom of the settler, was maintained concomitantly with a complete removal of the N and P supplied via centrate.

Optimization of COD, nitrate-N and phosphorus removal from hatchery wastewater with acclimatized mixed culture

The goal of this study is to optimize the condition of the pollutant removal process by using acclimatized mixed culture (AMC) in the treatment of contaminated waste from the hatchery industry. The removal of chemical oxygen demand (COD), nitrate-N, and total phosphorus was optimized using a central composite design and the Response Surface Methodology (RSM) with two parameters: AMC content and retention time (days). Each factor had a range value of 15%–35% AMC content and a retention time of 3–5 days, with COD, nitrate-N, and total phosphorus removal as responses. Prior to experimentation, the synthetic wastewater was prepared, and the mixed cultures were acclimatized. In 13 runs, the experiment was carried out in accordance with the setup created by the Design-Expert software. The sample was tested for COD, nitrate-N, and total phosphorus using a Hach spectrophotometer. The findings show a strong relationship between predicted and experimental COD, nitrate-N, and total phosphorus removal values. At optimum conditions of 29% AMC content and 4 days of retention time, removal of COD, nitrate-N, and total phosphorus was observed to be 28%, 80% and 36%, respectively. The discovery also revealed that maximum values of removal of 62% COD, 94% nitrate-N, and 46% total phosphorus could be obtained under various optimum conditions. The study shows that, the acclimatized mixed culture (AMC) can be used as a potential biological wastewater treatment as well as a natural removal of COD, nitrate-N, and total phosphorus.

Lead (Pb) removal from contaminated water using constructed wetland planted with Scirpus grossus: Optimization using response surface methodology (RSM) and assessment of rhizobacterial addition

Lead (Pb) is one of the toxic heavy metals that pollute the environment as a result of industrial activities. This study aims to optimize Pb removal from water by using horizontal free surface flow constructed wetland (HFSFCW) planted with Scirpus grossus. Optimization was conducted using response surface methodology (RSM) under Box–Behnken design with the operational parameters of initial Pb concentration, retention time, and aeration. Optimization results showed that 37 mg/L of initial Pb concentration, 32 days of retention time, and no aeration were the optimum conditions for Pb removal by using the systems. Validation test was run under two different conditions, namely, non-bioaugmented and bioaugmented with rhizobacteria (Bacillus cereus, B. pumilus, B. subtilis, Brevibacillus choshinensis, and Rhodococcus rhodochrous). Results of the validation test showed that Pb removal in water achieved 99.99% efficiency with 0.2% error from the RSM prediction, while the adsorption of Pb by plants reached 5160.18 mg/kg with 10.6% error from the RSM prediction. The bioaugmentation of the five rhizobacterial species showed a slight improvement in Pb removal from water and Pb adsorption by plants. However, no significant improvement was achieved (p < 0.05). Overall results suggested that operating the HFSFCW under optimum conditions with no bioaugmentation might be a feasible choice for the treatment of Pb-contaminated water.

Anaerobic co-digestion of chicken manure with energy crop residues for biogas production

Biogas or bio-methane is an alternative energy source produced by anaerobic digestion (AD) technology whereby the organic matter is degraded by naturally present microorganisms and converted into a combustible gas. This paper focus on the utilization of anaerobic codigestion (AcoD) method since biogas yield so far remains minimum based on mono-digestion alone due to low energy content. In this work, empty fruit bunch (EFB), oil palm frond (OPF) and sugarcane bagasse (SB) are being used as co-digestion additive since energy crop residues are known for its high carbon and energy content to enhance the process. A series of five 1.5L reactors were set up for a mesophilic condition at temperature 40°C, with initial pH range of 7-8, for 60 days of retention time. The mono-digestion reactor of chicken manure is labelled as DC1, and the co-digestion reactors with sugarcane bagasse, OPF and EFB are labelled as DSB, DOPF and DEFB, respectively. The recorded C/N ratio of co-digestion reactors were improved to be in a favourable range of 15 to 35 with DSB being the highest at 17.74 compared to that of control reactor at 11.35. As a result, total biogas production for DSB increases up to 36% due to its significantly high carbon content from sugarcane bagasse that provide stability for the bacterial growth and its activities. Sugarcane bagasse act as a good carbon source for the AD system, thus enhance the methane production. On the other hand, DOPF and DEFB give 13% and 41% lesser total biogas volume, however, produces much higher methane concentration compared to the control reactor. This shows that DOPF and DEFB give a higher methane yield which defines the more stability and efficiency of digestion process.

Sustainable anaerobic digestion of euphorbiaceae waste for biogas production: Effects of feedstock variation

Anaerobic digestion (AD) refers to the biological process which can convert organic substrates to biogas in the absence of oxygen. The aim of this study was to determine the capability of feedstock to produce biogas and to quantify the biogas yield from different feedstocks. A co-digestion approach was carried out in a continuous stirred tank reactor operated under mesophilic conditions and at a constant organic loading rate of 0.0756 g COD/ L.day, with a hydraulic retention time of 25 days. For comparison, mono-digestion was also included in the experimental work. 2 L working volumes were used throughout the experimental work. The seed culture was obtained from composting as substrate digestion. When the feedstock was added to seeding, the biogas started to emit after three days of retention time. The highest volume of biogas was observed when the seeding volume used for 1000 mL. However, the lowest volume of biogas yield was obtained from both co-digestion reactors, with a value of 340 mL. For methane yield, the highest methane production rate was 0.16 L CH4/mg. The COD with yield was at 8.6% and the lowest was at 0.5%. The highest quantity of methane was obtained from a reactor of Euphorbiaceae peel with added seeding, while the lowest methane yield came from a reactor of Euphorbiaceae stems with added seeding. In this study, sodium bicarbonate (NaHCO3) was used as a buffering solution to correct the pH in the reactor if the reactor condition was found to be in a souring or acidic condition.

Hydro-biological characterization and efficiency of natural waste stabilization ponds in a desert climate (city of Assa, Southern Morocco)

Abstract The city of Assa is located in a Saharian area characterized by an arid climate and water scarcity. Like any other Saharian city in a developing country, the city is facing the challenges of rapid urbanization and the need to improve wastewater treatment and management. The main objective of this work is to assess the performance of waste stabilization ponds in an arid area. This evaluation concerns microbiological and physico-chemical monitoring over three and twelve months respectively. Microbiological results indicate bacterial elimination rates of over 90% in autumn–winter due to the effectiveness of facultative ponds with 20–25 days of retention time, water clarity, ponds depth, and high sunlight exposure and penetration. Physico-chemical parameters surpass the Moroccan standards for reuse except Ph and T0 by 20–30%, this wastewater is relatively loaded with various pollutants, especially high organic load and low oxygen content. Statistical analysis has been made by principal component analysis (PCA), and confirms that dissolved oxygen, total suspended solids, COD and BOD5 do not reach the threshold for discharge into the natural environment, and moreover their reuse. For the improvement of the quality of these waters, it is legitimate to provide an upgrade of this plant by a tertiary treatment with maturation ponds.

Design, Construction and Production of Small Scale Energy Generation Plant using Indigenous Resources

Developing countries like Pakistan are in serious energy crisis. Renewable energy resources are the best alternative for conventional energy sources. The use of indigenous resources to produce bioenergy is an excellent solution to meet the energy needs of developing countries. The aim of the study was to design, construct and production of bioenergy generation from indigenous resources to fulfil bioenergy requirement for electricity, cooking and heating. This research introduces the Best Available Technology (BAT) and bioenergy plant was constructed with local materials at minimum cost to avoid economic burden on bioenergy production cost. An underground bio-digester unit with a volume of 10 cubic meter (7 m3 bioenergy digester tank plus 3 m3 bioenergy gas cap/holder) has been installed. The daily feed was approximately 160 kilogram of cow slurry (80 kg cow dung plus 80 litres/kg water). The retention period was approximately 44 days and the reported seasonal temperature was approximately 24˚C - 32˚C. The unit was thermally insulated, so the fluctuation in temperature was slightly about ±2˚C. In experimental setup, indigenous biomass resources were mixed with water in a mixing chamber. Whole mixture enters into digester through the inlet pipe and regularly feed up to selected retention time. Anaerobic bacteria decompose the biomass in the digester and produce bioenergy. A simulation was performed to estimate relevant model parameters from experimental data. The proposed model can predict methane production behaviour from some key indicators (such as organic matter and VFAs) in the anaerobic digestion process. Results obtained from the experiment showed that the plant could generate average volume of 3.18 m3 of bioenergy biogas at average pressure of 170 mbar in a day. Results also revealed that the rate of bioenergy generation increase with respect to time from 33 to 44 days of retention time, the pressure of bioenergy generated increase from 35 mbar to 175 mbar. From the results, it was observable that the more the pressure in the chamber, the more the volume of bioenergy generated; thus, at 175 mbars, it produced maximum volume of 3.2 m3 of bioenergy.

Vertical Subsurface Flow (VSSF) constructed wetland for domestic wastewater treatment

Vertical Subsurface Flow Constructed Wetland (VSSF) is appraised to become an alternative solution for treating domestic wastewater effectively and efficiently. The system which imitates the natural wetland concept is able to reduce organic material and nutrients in wastewater; therefore, it will be more feasible to be discharged to the environment. This study aimed to compare which species is more recommended to be applied for reducing organic material and nutrients in domestic wastewater. This experimental study applied four treatments, i.e 1) control (unplanted), 2) single species Iris pseudacorus, 3) single species Echinodorus palaefolius, and 4) combination (Iris pseudacorus and Echinodorus palaefolius) with three days of retention time. The application of those plants aims for holding the role in increasing wastewater quality and adding aesthetic impression at once. The plants were planted on VSSF media, in relatively same of weight and size to compare their effectiveness in decreasing organic and inorganic load. The parameters measured pervade TDS, pH, BOD5, COD, Nitrate, and Phosphate. The plants’ condition was also observed during and after the system worked. The result showed that the best average value of effectiveness for each of parameters: COD by combination treatment (50.76%), BOD5 by single I. pseudacorus (30.15%), Nitrate by single E. palaefolius (58.06%), Phosphate by single E. palaefolius (99.5%), and TDS by E.palaefolius (3.25%). The result showed that there was a significant difference of Nitrate and Phosphate reduction between control and three other treatments, while pH parameter showed non-significant change among them. In term of performance, I.pseudacorus seemed showed a preferable achievement.

Mesophilic co-digestion of municipal solid waste and sewage sludge: Effect of mixing ratio, total solids, and alkaline pretreatment

A large number of biogas plants feeding with municipal solid waste (MSW) are installed throughout the world. However, researches are widely conducted with the aim of maximizing the process yield, in order to make it more comparable with fossil fuels. In the present paper, biomethane potential test (BMP) assays (37 °C) were conducted to maximize the biomethane production from anaerobic digestion (AD) of municipal solid waste (MSW) under different mixing ratios with sewage sludge (SS) (50:50, 60:40, 80:20, and 90:10), the total solid (TS) concentrations (5%, 10%, 15%, and 20%), and pretreatment with sodium hydroxide. Increase in SS ratio up to 40% led to a substantial increase in biomethane yield. After 18 days of retention time, 90% of the methane (280 NmL/g VS) was achieved. The results showed that the methane yield in liquid anaerobic digestion (L-AD) (5%-10% TS) was greater than high-solids anaerobic digestion (HS-AD) (15%-20% TS). Biomethane yield was increased up to 18% with sodium hydroxide pretreatment. The findings shows that such optimization framework can generally increase the biomethane yield up to 57%.

Determination of the fractions of syntrophically oxidized acetate in a mesophilic methanogenic reactor through an 12C and 13C isotope-based kinetic model

In order to accurately describe the carbon flow in anaerobic digestion processes, this work investigates the acetate degradation pathways through the use of stable carbon isotope analysis and a mathematical model. Batch assays using labeled 13C acetate were employed to distinguish the acetate consumption through methanogenic Archaea and acetate-oxidizing Bacteria. Suspended and sessile biomass, with over 400 days of retention time, from a mesophilic (36.5 °C) upflow anaerobic filter was used as inocula in these assays. A three-process model for acetoclastic methanogenesis and syntrophic acetate oxidation (SAO) was developed to allow for a precise quantification of the SAO contribution. The model distinguishes carbon atoms in light and heavy isotopes, 12C and 13C, respectively, which permitted the simulation of the isotope ratios variation in addition to gas production, gas composition and acetate concentrations. The model indicated oxidized fractions of acetate between 7 and 18%. Due to the low free ammonia inhibition potential for the acetoclastic methanogens in these assays these findings point to the biomass retention times as a driven factor for the SAO pathway. The isotope-based kinetic model developed here also describes the δ13C variations in unlabeled assays accurately and has the potential to determine biological 13C fractionation factors.

Removal Efficiency of Ammoniacal Nitrogen from Palm Oil Mill Effluent (POME) by Varying Soil Properties

Palm Oil Mill Effluent (POME) contains large amounts of organic matters and nutrients. Instead of discharging into oxidation ponds, POME can be used as an alternative option to replace inorganic fertilizers which have been known to increase the hardness and acidity of the soil over time. This study investigated the effect of different soil properties on the ammoniacal nitrogen removal efficiencies in POME. The ammoniacal nitrogen removal efficiencies from three mediums over 7 days of retention times were studied. Medium I contained major amount of sand, whereas medium II contained major amounts of clay and lastly medium III contained large amounts of silt and clay. The results showed that medium II produced the highest removal efficiency of ammoniacal nitrogen in POME, with the average removal efficiency of 77±5.1%. The average values of removal efficiencies obtained from mediums I and III were 61±6.2 and 58±11.3%, respectively. In addition, the removal efficiency of ammoniacal nitrogen increased slowly with the retention time. Medium II recorded the highest removal rate (k = 0.0897 dayG1) compared to mediums I (k = 0.0435 dayG1) and III (k = 0.0492 dayG1). The mechanism of removal ammoniacal nitrogen from the medium occurred via absorption by the soil particle.

Spatial and temporal variations of microbial community in a mixed plug‐flow loop reactor fed with dairy manure

Mixed plug-flow loop reactor (MPFLR) has been widely adopted by the US dairy farms to convert cattle manure to biogas. However, the microbiome in MPFLR digesters remains unexplored. In this study, the microbiome in a MPFLR digester operated on a mega-dairy farm was examined thrice over a 2 month period. Within 23 days of retention time, 55–70% of total manure solid was digested. Except for a few minor volatile fatty acids (VFAs), total VFA concentration and pH remained similar along the course of the digester and over time. Metagenomic analysis showed that although with some temporal variations, the bacterial community was rather stable spatially in the digester. The methanogenic community was also stable both spatially and temporally in the digester. Among methanogens, genus Methanosaeta dominated in the digester. Quantitative polymerase chain reaction (qPCR) analysis and metagenomic analysis yielded different relative abundance of individual genera of methanogens, especially for Methanobacterium, which was predominant based on qPCR analysis but undetectable by metagenomics. Collectively, the results showed that only small microbial and chemical gradients existed within the digester, and the digestion process occurred similarly throughout the MPFLR digester. The findings of this study may help improve the operation and design of this type of manure digesters.

Effect of Phragmites australis and Typha latifolia on biofiltration of heavy metals from secondary treated effluent

The present work deals with a promising approach for the removal of heavy metals from secondary treated wastewater using aquatic plants, which are economic and effective in separating metals from polluted water. Since the conventional sewage treatment processes were inefficient to remove heavy metals from wastewater, batch experiments of Phragmites australis, Typha latifolia and P. australis and T. latifolia grown in association and reference (unplanted) were carried out for 15 days of retention time for the removal of copper (Cu), cadmium (Cd), chromium (Cr), nickel (Ni), iron (Fe), lead (Pb), and zinc (Zn) from the secondary treated effluent. Significantly, higher removal of the heavy metals in planted set than the reference revealed role of plants in their removal (analysis of variance, p < 0.05). Higher removal of Cr, Fe, and Zn (66.2 ± 3.5, 70.6 ± 1.2, and 71.6 ± 3.9 %) in the combination of the P. australis and T. latifolia than their individual culture suggested synergistic effect of both the plants in the removal of these metals. Positive relationship was observed between retention time and the removal of heavy metals. Mass balance equation has revealed that the loss of heavy metals in wastewater was equivalent to the net accumulation of heavy metals in plant and loss of heavy metals in natural degradation. P. australis showed higher accumulative capacities for Cu, Cd, Cr, Ni, Fe, and Pb than those of T. latifolia. The P. australis and T. latifolia grown in association might be utilized for the heavy metal removal in the tropical environment.