Organic Overloading Research Articles

Comportamento da produção de espécies reativas de oxigênio em miocárdio de ratos submetidos a treinamento de baixa intensidade em diferentes temperaturas

INTRODUÇÃO: A prática de exercício físico proporciona aumento da produção de espécies reativas de oxigênio (ERO) resultantes do metabolismo aeróbio e, gera uma quantidade significativa de calor, em conseqüência da produção de energia, resultando em sobrecarga orgânica. A associação entre ERO e exercício, e entre exercício e variações da temperatura ambiente têm sido estudadas, contudo, há escassez de informações que considere a associação entre produção de radicais livres no miocárdio e atividade física em temperatura elevada. OBJETIVO: Comparar a produção de ERO em miocárdio de ratos submetidos ao treinamento de baixa intensidade em diferentes temperaturas. MÉTODOS: Foram utilizados 20 ratos Wistar, machos, jovens, peso (250 a 280g), divididos em quatro grupos: G1 (n = 5) expostos ao treinamento e calor (39º ± 1C); G2 (n = 5) expostos somente ao calor durante o mesmo período de G1, sem treinamento; G3 (n = 5) expostos ao treinamento em temperatura ambiente (22º ± 1C); G4 (n = 5) expostos à temperatura ambiente sem treinamento. O treinamento foi realizado em esteira rolante climatizada por cinco semanas, evoluindo 5 minutos a cada duas sessões finalizando em 60 minutos em baixa intensidade 8m/min. O ambiente foi controlado entre 39 ± 1ºC e 22 ± 1ºC e entre 40 e 60 % de umidade relativa. A lipoperoxidação foi avaliada por Quimiluminescência (QL). A análise dos dados foi realizada a partir do teste Two Way ANOVA para análise da QL e t de student para a Capacidade Antioxidante Total (TRAP). RESULTADOS: A análise da QL revelou uma curva de emissão de luz significantemente mais baixa para o grupo exposto ao exercício em normotermia comparado aos sedentários mantidos no calor. A análise da TRAP mostrou diminuição em todos os grupos experimentais em relação ao G4. CONCLUSÃO: Concluiu-se que houve níveis menores de produção de ERO nos grupos submetidos somente ao calor ou somente ao exercício.

Fuzzy-Based Control of an Anaerobic Reactor Treating Wastewaters Containing Ethanol and Carbohydrates

In this work, a fuzzy logic-based system for diagnosis and control of an anaerobic wastewater treatment plant was developed. Three variables (methane production, hydrogen concentration in the gas phase, and intermediate alkalinity/total alkalinity ratio) were selected, according to previous works, as the more adequate for organic overload identification. The diagnosis and control system was developed using expert's knowledge related with normal or overload process states for establishing a set of rules considering the selected variables. The control system computes the feed flow rate for adjusting the organic load applied to the reactor. The control law is based on a response surface obtained according to fuzzy inference Mamdani methodology. The diagnosis and control system was validated at three different levels: (a) simulation with ADM1 (wastewater containing ethanol); (b) open-loop methodology using experimental data from a hybrid upflow sludge bed-filter (USBF) anaerobic pilot plant treating a wastewater containing ethanol; and (c) closed-loop control of a USBF pilot plant treating wastewater containing carbohydrates. The proposed system diagnoses correctly the different episodes, and it demonstrated a high reliability, supplying an adequate control action to achieve the desired set point as well as to manage a sudden change in influent COD. Moreover, the performance of the developed system can depend slightly of the noise in the measured variables used for determining the process state.

Characteristics of Granular Sludge Developed in an Upflow Anaerobic Sludge Fixed‐Film Bioreactor Treating Palm Oil Mill Effluent

In the present study, characteristics of the granular sludge (including physical characteristics under stable conditions and process shocks arising from suspended solid overload, soluble organic overload, and high temperature; biological activity; and sludge kinetic evaluation in a batch experiment) developed in an upflow anaerobic sludge blanket fixed-film reactor for palm oil mill effluent (POME) treatment was investigated. The main aim of this work was to provide suitable understanding of POME anaerobic digestion using such a granular sludge reactor, particularly with respect to granule structure at various operating conditions. The morphological changes in granular sludge resulting from various operational conditions was studied using scanning electron microscopy and transmission electron microscopy images. It was shown that the developed granules consisted of densely packed rod- (Methanosaeta-like microorganism; predominant) and cocci- (Methanosarsina) shaped microorganisms. Methanosaeta aggregates functioned as nucleation centers that initiated granule development of POME-degrading granules. Under the suspended solid overload condition, most of the granules were covered with a thin layer of fiberlike suspended solids, so that the granule color changed to brown and the sludge volume index also increased to 24.5 from 12 to 15 mL/g, which caused a large amount of sludge washout. Some of the granules were disintegrated because of an acidified environment, which originated from acidogenesis of high influent organic load (29 g chemical oxygen demand [COD]/L d). At 60 degrees C, the rate of biomass washout increased, as a result of disintegration of the outer layer of the granules. In the biological activity test, approximately 95% COD removal was achieved within 72 hours, with an initial COD removal rate of 3.5 g COD/L d. During POME digestion, 275 mg calcium carbonate/L bicarbonate alkalinity was produced per 1000 mg COD(removed)/ L. A consecutive reaction kinetic model was used to simulate the data obtained from the sludge activity in the batch experiment. The mathematical model gave a good fit with the experimental results (R2 > 0.93). The slowest step was modeled to be the acidification step, with a rate constant between 0.015 and 0.083 hours(-1), while the rate constant for the methanogenic step was obtained to be between 0.218 and 0.361 hours(-1).

EFFECT OF TRYPTONE AND AMMONIA ON THE BIOGAS PROCESS IN CONTINUOUSLY STIRRED TANK REACTORS TREATING CATTLE MANURE

Two thermophilic continuously stirred tank reactors, R1 and R2, were subject to pulses of tryptone and ammonia. R1 was operated at an ammonia-N concentration of 3.0 g l-1 and R2 was operated at an ammonia-N concentration of 1.7 g l-1. Shock loads of tryptone (10 g l-1, 10 g l-1, 15 g l-1) had an immediate stimulating effect on methanogenesis for both reactors illustrated by significant peaks in methane production but also led to an organic overloading illustrated by a steep increase in volatile fatty acids (VFA) concentration. Three days after the pulses a second peak in acetate concentration and a decrease in methane production indicated an ammonia-inhibition of the acetoclastic methanogens. During the pulses of tryptone the performance of R1 was slightly more affected than R2. Pulses of ammonia (0.79 g l-1 as N) resulted in a decrease in methane production of both reactors but no immediate increases in VFA concentrations was observed illustrating that the ammonia inhibition during this experiment was an overall inhibition of the biogas process and not only an inhibition of the methanogens.

On‐line near infrared monitoring of glycerol‐boosted anaerobic digestion processes: Evaluation of process analytical technologies

A study of NIR as a tool for process monitoring of thermophilic anaerobic digestion boosted by glycerol has been carried out, aiming at developing simple and robust Process Analytical Technology modalities for on-line surveillance in full scale biogas plants. Three 5 L laboratory fermenters equipped with on-line NIR sensor and special sampling stations were used as a basis for chemometric multivariate calibration. NIR characterisation using Transflexive Embedded Near Infra-Red Sensor (TENIRS) equipment integrated into an external recurrent loop on the fermentation reactors, allows for representative sampling, of the highly heterogeneous fermentation bio slurries. Glycerol is an important by-product from the increasing European bio-diesel production. Glycerol addition can boost biogas yields, if not exceeding a limiting 5-7 g L(-1) concentration inside the fermenter-further increase can cause strong imbalance in the anaerobic digestion process. A secondary objective was to evaluate the effect of addition of glycerol, in a spiking experiment which introduced increasing organic overloading as monitored by volatile fatty acids (VFA) levels. High correlation between on-line NIR determinations of glycerol and VFA contents has been documented. Chemometric regression models (PLS) between glycerol and NIR spectra needed no outlier removals and only one PLS-component was required. Test set validation resulted in excellent measures of prediction performance, precision: r(2) = 0.96 and accuracy = 1.04, slope of predicted versus reference fitting. Similar prediction statistics for acetic acid, iso-butanoic acid and total VFA proves that process NIR spectroscopy is able to quantify all pertinent levels of both volatile fatty acids and glycerol.

Winery effluent treatment at an anaerobic hybrid USBF pilot plant under normal and abnormal operation

A 1.1 m3 hybrid USBF fully instrumented pilot plant has been used for the treatment of diluted wine for four years. In this work, the performance of the wastewater treatment plant (WWTP) during start up and operation (normal operation and overload experiments) is shown. A complete description of the treatment process behaviour (gas and liquid phase composition and anaerobic sludge characteristics) is given by on-line and off-line monitoring of 28 process variables. The results presented here demonstrate the reliability of this technology for the treatment of wastewater from seasonal processes, such as winery wastewaters, during a long period of time (four years). Furthermore, the USBF reactor presented very short start up periods after short and long shut down of the WWTP and rapidly turned back to normal operation after suffering a complete destabilization due to organic overload. Both effluent and biogas were of good quality. Dissolved organic carbon concentration in the effluent was always lower than 100 mg DOC l(-1) under normal operation, while methane concentration in the biogas was in the range 70-74%, making it suitable for energy recovering.

Regulation and optimization of the biogas process: Propionate as a key parameter

Abstract The use of volatile fatty acids (VFA) as process indicators in biogas reactors treating manure together with industrial waste was studied. At a full-scale biogas plant, an online VFA sensor was installed in order to study VFA dynamics during stable and unstable operation. During stable operation acetate increased significantly during the feeding periods from a level of 2–4 to 12–17 mM, but the concentration generally dropped to about the same level as before feeding. The fluctuations in the propionate were more moderate than for acetate but the average level rose during 1 week of operation from 0.6 to 2.9 mM. A process disturbance caused by overloading with industrial waste was reflected by a significant increase in all VFA concentrations. During the recovery of the process, the return of propionate back to the steady-state level was 2–3 days slower than any other VFA and propionate could best describe the normalizing of the process. In a lab-scale continuously stirred tank reactor experiment, with manure as main substrate, the prospective of using either propionate concentration or methane production as single process indicators was studied. Propionate was found to be the best indicator. Thus, a process breakdown caused by organic overloading with meat and bone meal and lipids was indicated by changes in propionate concentration 12–18 days before a decrease in methane production was observed. Furthermore, a more efficient and stable utilization of the substrate was observed when propionate was used as process indicator.

Semi-continuous co-digestion of solid slaughterhouse waste, manure, and fruit and vegetable waste

The potential of semi-continuous mesophilic anaerobic digestion (AD) for the treatment of solid slaughterhouse waste, fruit-vegetable wastes, and manure in a co-digestion process has been experimentally evaluated. A study was made at laboratory scale using four 2 L reactors working semi-continuously at 35 °C. The effect of the organic loading rate (OLR) was initially examined (using equal proportion of the three components on a volatile solids, VS, basis). Anaerobic co-digestion with OLRs in the range 0.3–1.3 kg VS m −3 d −1 resulted in methane yields of 0.3 m 3 kg −1 VS added, with a methane content in the biogas of 54–56%. However, at a further increased loading, the biogas production decreased and there was a reduction in the methane yield indicating organic overload or insufficient buffering capacity in the digester. In the second part of the investigation, co-digestion was studied in a mixture experiment using 10 different feed compositions. The digestion of mixed substrates was in all cases better than that of the pure substrates, with the exception of the mixture of equal amounts of (VS/VS) solid cattle–swine slaughterhouse waste (SCSSW) with fruit and vegetable waste (FVW). For all other mixtures, the steady-state biogas production for the mixture was in the range 1.1–1.6 L d −1, with a methane content of 50–57% after 60 days of operation. The methane yields were in the range 0.27–0.35 m 3 kg −1 VS added and VS reductions of more than 50% and up to 67% were obtained.

Temperature-Based Control of an Anaerobic Reactor Using a Multi-Model Observer-Based Estimator

This study presents a temperature-based control strategy for the stabilization of an anaerobic reactor during organic overloads. To prove feasibility of the proposed approach the rate of methane production was followed in batch activity tests and reactor runs during mesophilic-thermophilic transitions. Within the first 0.25-6 h of temperature augmentation, an increase in the rate of methane production was observed with higher rates measured under thermophilic (above 40 degrees C) conditions. However, 24 h after startup both in batch tests and reactor runs, the rate of methane production under thermophilic conditions was inferior to that under optimal mesophilic conditions (35 degrees C). Following these results, a control strategy based on short-term augmentation of the reactor temperature was proposed and tested in a 10 L UASB reactor. The control strategy employed a multi-model observer-based estimator to stabilize the effluent COD concentration during organic overloads. The temperature-based control resulted in an increased methanization rate and improved reactor stability overall.

Food-Service Establishment Wastewater Characterization

Food-service establishments that use on-site wastewater treatment systems are experiencing pretreatment system and/or drain field hydraulic and/or organic overloading. This study included characterization of four wastewater parameters (five-day biochemical oxygen demand [BOD5]; total suspended solids [TSS]; food, oil, and grease [FOG]; and flow) from 28 restaurants located in Texas during June, July, and August 2002. The field sampling methodology included taking a grab sample from each restaurant for 6 consecutive days at approximately the same time each day, followed by a 2-week break, and then sampling again for another 6 consecutive days, for a total of 12 samples per restaurant and 336 total observations. The analysis indicates higher organic (BOD5) and hydraulic values for restaurants than those typically found in the literature. The design values for this study for BOD5, TSS, FOG, and flow were 1523, 664, and 197 mg/L, and 96 L/day-seat respectively, which captured over 80% of the data collected.

ADM1 application for tuning and performance analysis of a multi-model observer-based estimator

Anaerobic digestion model no.1 (ADM1) was used for tuning and performance analysis of the multi-model observer based estimator (mmOBE). The mmOBE was based on the variable structure model (VSM) of the anaerobic digestion model, which consists of several local submodels, each of which describes a typical process state. Depending on the hydraulic retention time, ADM1 simulated the methanogenic, organic overload, and acidogenic states of the process. These simulations allowed for optimising tunable parameters of the mmOBE. Owing to relatively slow process dynamics, a data acquisition interval as large as one day was sufficient to obtain acceptable accuracy. The simulations of mmOBE performance showed excellent rate of mmOBE convergence to ADM1 outputs. Moreover, mmOBE successfully estimated key kinetic parameters, such as maximal transformation rates of CODs, VFAs, and methane. These estimations can be used in the development of the advanced knowledge-based process system, which uses both available measurements and estimations of key kinetic parameters for extended diagnosis of failures and process trend analysis.

Application of a VSM-Based Process Control to a Bench-Scale Anaerobic Digestor

A variable structure model (VSM) was used for online control of a bench-scale anaerobic digestor. The VSM consisted of three submodels, which described the methanogenic, organic overload, and acidogenic states of the digestion process. Submodel activation was handled by a knowledge-based system, which used online measurements of the digestor pH and biogas composition to identify the process state and thereby select an appropriate leading submodel. Separate controllers were designed for each submodel, but only the controller corresponding to the leading submodel was applied at each instant. Experimental validation of the VSM-based feedback process control in a 5-L anaerobic digestor showed a stable process performance under various operating conditions.

Transient State Detection and Prediction of Organic Overload in Anaerobic Digestion Process Using Statistical Tools

Anaerobic wastewater treatment is a very complex system, which involves a great number of process (bioprocess as well as physicochemical process) running in parallel and series. This means that multivariable analysis is needed for state identification of such a process. The objective of this work is to use statistical multivariable tools to detect different overloads (non stable conditions) in an anaerobic digester and select the most influencing variables on state detection. It is also considered to build a predictor for these variables using both linear and non linear techniques. Factorial discriminant analysis (FDA) is a linear methodology used for classifying multivariate data in a less dimension space, for example a two dimension plane. By the other hand, artificial neural networks (ANN) can be trained to classify a group of data with the advantage of being a non linear tool. Both techniques were compared for organic overload classification by the analysis of 7 variables of a wastewater treatment process carried out in an anaerobic reactor. Similar classification capability was found for both techniques. In spite of FDA simplicity, this tool seems to have similar performance than ANN. By the analysis of FDA coefficients and the variables variances, it was possible to determine the main variable for classification. It was found that hydrogen flowrate (QH 2 ) and methane flowrate (QCH 4 ) are the most influencing variables for classification. In order to forecast the state of the process it was considered interesting to by able to predict these two key variables. Time series analysis (a linear model) and neural networks (non linear model) were used for 1 hour prediction of QH 2 and QCH 4 . The validation error for both techniques were very small, 2.5% and 5.5% for times series analysis and neural network, respectively. Linear models seem to give as good results as non linear and more complex models (neural networks) for classification and prediction

Dynamic evaluation of a fixed bed anaerobic digestion process in response to organic overloads and toxicant shock loads

This paper details a dynamic evaluation of a 1 m3 fixed bed anaerobic digestion reactor in response to organic overloads and toxicant shock loads. Raw industrial wine distillery wastewater was used as a reference substrate and several disturbances were applied to the process: (i) organic overloads with and without pH regulation in the feeding line, (ii) adding of ammonia in the input wastewater. The purpose of this study was to assess, using on-line instrumentation, the robustness of a fixed bed anaerobic digester. Anaerobic digestion processes have the reputation of being difficult to operate and prone to process instability due to external disturbances and the objective of this study was to demonstrate the possibility of such a reactor configuration for industrial use.

Start‐up and recovery of a biogas‐reactor using a hierarchical neural network‐based control tool

AbstractDue to its intricate internal biological structure the process of anaerobic digestion is difficult to control. The aim of any applied process control is to maximize methane production and minimize the chemical oxygen demand of the effluent and surplus sludge production. Of special interest is the start‐up and adaptation phase of the bioreactor and the recovery of the biocoenose after a toxic event. It is shown that the anaerobic digestion of surplus sludge can be effectively modeled by means of a hierarchical system of neural networks and a prediction of biogas production and composition can be made several time‐steps in advance. Thus it was possible to optimally control the loading rate during the start‐up of a non‐adapted system and to recover an anaerobic reactor after a period of heavy organic overload. During the controlled period an optimal feeding profile that allowed a minimum loading rate of 6 kg COD m−3 d−1 to be maintained was found. Maximum loading rates higher than 12 kg COD m−3 d−1 were often reached without destabilizing the system. The control strategy resulted simultaneously in a high level of gas production of about 3 m3biogas m−3reactor and a methane content in the biogas of about 70%. To visualize the effects of the control strategy on the reactor's operational space the data were processed using a data‐mining program based on Kohonen Self‐Organizing Maps. Copyright © 2003 Society of Chemical Industry

Removal of Organic Pollutants and Metabolic Adaptation of Microorganisms by Micro-aeration

Aerobic systems are high rate processes for wastewater treatment, but they consume much power for aeration. Several low-cost anaerobic systems have been developed for mid- and low-income countries. The removal efficiencies of nutrients, particulate matter, and pathogens are not satisfactory for the anaerobic systems. Micro-aeration is a type of low-cost aerobic application which enhances oxygen transfer through water surface. Trickling was found the most efficient method of micro-aeration and batch experiments were performed to evaluate the effectiveness. When soluble organic carbon was removed, ORP7 (redox potential rectified to pH at 7) were around −120 or +260 mV. When soluble organic carbon increased due to organic overload, ORP7 was around +30 mV. At +30 mV, carbon fraction of biomass increased to 0.54 (higher than average value of 0.46). It was presumable that the ORP7 of −120, +260, and +30 mV were anaerobic, aerobic, and internal storage mode, respectively. Maximum reaction rate of aerobic condition was four times as high as that of anaerobic condition. At internal storage mode, the rate was halved from aerobic mode. It is concluded that microorganisms adapt the metabolic systems to conform to the redox environment, which can be evaluated by ORP. Organic overload results metabolic shift to internal storage mode which retards mineralization of organic matter.

An integrated approach to waste stabilization pond design in Marrakech

Most wastewater treatment programs in Morocco are directed towards reuse of the effluent in irrigation. A ten-year running of an experimental two-stabilization-pond system in Marrakech showed that despite retention times around 50 days, the quality of the effluent corresponded to a restrictive irrigation reuse (B category according to the WHO guidelines). This quality can be achieved even with BOD loading reaching 780-1000 kg BOD / ha.d in one anoxic stabilization pond with a depth of 2.3 m and a retention time of 9.5 days. This primary anoxic pond did not show signs of organic matter over-loading with an active algae population, a pH all the time higher than 7 and a nematode egg concentration lower than 1 egg/L. The performance of such a system in terms of organic matter removal can be evaluated using a linear relation of the same type as the one proposed by Mac Gary and Pescod but with lower removal efficiency. However, nitrogen levels were still high with a concentration above FAO irrigation standards and can lead to groundwater quality degradation. We proposed an integrated approach to stabilization pond design that can be based on the required effluent quality to protect both public health (WHO guidelines) and the receiving environment. Groundwater vulnerability maps should be drawn and evaluated for nitrogen and other pollutant tolerance before any wastewater treatment system design. Models for nitrogen removal in stabilization ponds should be combined with those already in use for organic matter and pathogenic organisms removal to allow design of systems that are aesthetically attractive, sanitarily safe and harmless to the receiving environment.

Anoxic ponds in the sugar cane industry: a case study from Colombia

Waste stabilisation ponds are a common technology used to treat sugar mill wastewaters in Colombia. Despite this there are problems related to biological process design and construction of these units. The situation with regards to operation and maintenance is far from satisfactory and also contributes to pond malfunctioning. In this sense, a pond system located at Providencia sugar mill on the southwest region of Colombia, South America was evaluated. The system comprises an anaerobic pond followed by a secondary anoxic pond. The whole system removes 73-82% of the BOD, with 53-70% occurring in the secondary anoxic pond, which is satisfactory despite the predominant conditions of organic overloading. However, TSS removal was low in comparison to BOD removal. The secondary anoxic pond proved to be an efficient treatment unit with the advantage of controlling odour release through photosynthetic bacterial activity. Land area requirements were less than those for green algal facultative ponds.

Monitoring the Inhibitory Effect of NaCl on Anaerobic Wastewater Treatment Processes by the Rantox Biosensor

The Rantox biosensor, designed for anaerobic process control and based on the response of acetoclastic methanogenic microorganisms to periodic organic overloads, was tested under variable operating conditions at laboratory scale. The aim was to detect the presence of an incoming inorganic toxic compound before any effect was observed in a digester under control. The experimental set-up, including the biosensor and the digester, was connected to an automated control system developed under a Labview® environment (the Rantox Virtual Instrument), and various operating conditions were tested in order to interface the plant with the software properly. Anaerobic sludges with different activities were used as active biomass in both reactors, and inhibition was simulated by different NaCl dosing procedures. The results confirmed the sensitivity and rapid response of the biosensor to unexpected inhibitors in the feed, and demonstrated the suitability of this instrument for continuous or semicontinuous monitoring of the influent to a digester in order to prevent intoxication of its biomass. Furthermore, inhibition due to NaCl was found to be independent of the salt addition procedure. A concentration of 15 g NaCl lreact. −1 caused a decrease in peak biogas production ranging between 26.6% and 43.1%, depending on the different biomass tested.

Methane production from low solid concentration liquid swine waste using conventional anaerobic fermentation

A study was conducted to determine the methane production characteristics of low concentration liquid swine waste using conventional dispersed growth anaerobic fermentation at 35°C. Raw waste was obtained from a conventional under floor flushing system and screened using an 18 mesh vibrating liquid–solid separator. The volatile solid (VS) concentration of the influent waste used in the study was 15 g/l. Hydraulic retention times (HRTs) of 5, 3, 2, and 1 days were replicated three times with one 300 l bench scale fermenter. Results from the study show that conversion to methane is practical for the 5 and 3 day HRT but that considerable stress occurred at the 2 day HRT. One replicate failed during the 2 day HRT and all three replicates failed at the 1 day HRT. Failure of digestion was determined based on steady-state gas production. Methane productivity (LCH 4/g VS added) ranged from 0.36 to 0.22 for the 5 and 2 day HRTs, respectively. VS reduction showed a high of 51.6% for the 5 day HRT and a low of 34.5% for the 2 day. Steady-state operating levels of ammonia and total volatile fatty acids (TVFA) suggest no inhibition from either at any of the HRTs. Alkalinity levels were low (1200–2000 mg/l as CaCO 3) when compared to digestion studies using longer HRTs. Although foaming occurred at the 2 and 1 day HRT, TVFA levels remained low (<700 mg/l as acetic) and pH was >7. This suggests the failure mechanism was bacterial washout, not organic overloading.