Cutting the Wastewater Peaks for Cyclic Batch Production Plants

This paper proposes systematic approaches for cutting the wastewater peaks generated in cyclic batch production plants in which wastewater generation rates and concentration are varied with time. To reduce the investment for the wastewater treatment unit or not to violate the discharge limits, the fluctuations of both flow rate and concentration of the wastewater generated need to be controlled or equalized. Buffer tanks (or basin) are commonly used to regulate the wastewater flow and concentration before the wastewater is sent to treatment units or discharge. The size of the buffer tank needs to be designed properly so that its size is minimized and still has enough capacity to handle various operating conditions. In this paper, conceptual approaches are presented to minimize the size of the buffer tank for either controlling wastewater flow rate or concentration. Mathematical models are proposed for controlling both flow rate and concentration.     

Online nonlinear sequential Bayesian estimation of a biological wastewater treatment process

Online estimation of unknown state variables is a key component in the accurate modelling of biological wastewater treatment processes due to a lack of reliable online measurement systems. The extended Kalman filter (EKF) algorithm has been widely applied for wastewater treatment processes. However, the series approximations in the EKF algorithm are not valid, because biological wastewater treatment processes are highly nonlinear with a time-varying characteristic. This work proposes an alternative online estimation approach using the sequential Monte Carlo (SMC) methods for recursive online state estimation of a biological sequencing batch reactor for wastewater treatment. SMC is an algorithm that makes it possible to recursively construct the posterior probability density of the state variables, with respect to all available measurements, through a random exploration of the states by entities called ‘particle’. In this work, the simplified and modified Activated Sludge Model No. 3 with nonlinear biological kinetic models is used as a process model and formulated in a dynamic state-space model applied to the SMC method. The performance of the SMC method for online state estimation applied to a biological sequencing batch reactor with online and offline measured data is encouraging. The results indicate that the SMC method could emerge as a powerful tool for solving online state and parameter estimation problems without any model linearization or restrictive assumptions pertaining to the type of nonlinear models for biological wastewater treatment processes.     

Biofilm reactors for industrial bioconversion processes: employing potential of enhanced reaction rates

This article describes the use of biofilm reactors for the production of various chemicals by fermentation and wastewater treatment. Biofilm formation is a natural process where microbial cells attach to the support (adsorbent) or form flocs/aggregates (also called granules) without use of chemicals and form thick layers of cells known as "biofilms." As a result of biofilm formation, cell densities in the reactor increase and cell concentrations as high as 74 gL^-1 can be achieved. The reactor configurations can be as simple as a batch reactor, continuous stirred tank reactor (CSTR), packed bed reactor (PBR), fluidized bed reactor (FBR), airlift reactor (ALR), upflow anaerobic sludge blanket (UASB) reactor, or any other suitable configuration. In UASB granular biofilm particles are used. This article demonstrates that reactor productivities in these reactors have been superior to any other reactor types. This article describes production of ethanol, butanol, lactic acid, acetic acid/vinegar, succinic acid, and fumaric acid in addition to wastewater treatment in the biofilm reactors. As the title suggests, biofilm reactors have high potential to be employed in biotechnology/bioconversion industry for viable economic reasons. In this article, various reactor types have been compared for the above bioconversion processes.     

Sequencing batch biofilter granular reactor for textile wastewater treatment

Textile wastewater is difficult to treat as it usually contains considerable amounts of different pollutants, which are often recalcitrant, toxic and inhibitory. Therefore, complex treatment schemes based on the sequence of various steps are usually required for an effective treatment. This explains why textile effluents are often treated in centralized plants and sometimes mixed with municipal wastewater. The adoption of new technologies for on-site treatment, instead, would be optimal, deeply reducing treatment costs. An innovative technology exhibiting several characteristics appropriate for the attainment of such a goal is sequencing batch biofilter granular reactor (SBBGR). To assess the suitability of this technology, two lab-scale reactors were operated, treating mixed municipal-textile wastewater and a pure textile effluent, respectively. Results have demonstrated that mixed wastewater can be successfully treated with very low hydraulic retention times (less than 10 hours). Furthermore, SBBGR shows to be an effective pre-treatment for textile wastewater for discharge into sewer systems. The economic evaluation of the process showed operative costs of 0.10 and 0.19 € per m(3) of mixed wastewater and textile wastewater, respectively.     

Development of anaerobic sludge bed (ASB) reactor technologies for domestic wastewater treatment: motives and perspectives

During the treatment of raw domestic wastewater in the upflow anaerobic sludge blanket (UASB) reactor, the suspended solids (SS) present in the wastewater tend to influence negatively the methanogenic activity and the chemical oxygen demand (COD) conversion efficiency. These problems led to the emergence of various anaerobic sludge bed systems such as the expanded granular sludge bed (EGSB), the upflow anaerobic sludge blanket (UASB)-septic tank, the hydrolysis upflow sludge bed (HUSB), the two-stage reactor and the anaerobic hybrid (AH) reactor. However, these systems have, like the UASB reactor, limited performance with regard to complete treatment (e.g., removal of pathogens). In this respect, a new integrated approach for the anaerobic treatment of domestic wastewater is suggested. This approach combines a UASB reactor and a conventional completely stirred tank reactor (CSTR) for the treatment of the wastewater low in SS and sedimented primary sludge, respectively. The principal advantages of the proposed system are energy recovery from organic waste in an environmentally friendly way; lowering the negative effect of suspended solids in the UASB reactor; production of a high quality effluent for irrigation; and prevention of odour problems.     

Enhancement of Anaerobic Digestion Using Particulate Growth Systems

Attached media reactors are used for enhancement of wastewater treatment processes including anaerobic condition. Selection of a suitable biofilm carrier is a compelling method to improve anaerobic digestion systems. This study investigates the performance of four fibrous biofilms installed in batch biogas reactors for treatment of cow manure. BioCords HS1, HS2, LS1, and LS2 are manufactured by Bishop Water Technologies, ON, Canada. Effluents and attached growth media were analyzed after batch experiment; methane production, methane yield, transfer efficiencies, organic and solid removal efficiencies, pH, and attached volatile suspended solid (VSS) were measured; VSS attached to biofilms mainly correlated with the specific surface area of each biofilm. Additionally, SEM (scanning electron microscopy) was used for further understanding of biofilm formation process for BioCords and the dissimilarity in their performance. The results indicated that BioCord LS2 had positive impact on achieving higher methane production and removal efficiencies compared to other support media utilized in batch reactors. It was also demonstrated from the experiment that BioCord LS2 potentially could generate higher methane production than conventional batch bioreactor.     

Upgrading of Existing Municipal Wastewater Treatment Plants with the “Non‐Conventional Low MLSS MBR Technology”

In the future, upgrading of existing wastewater treatment plants (wwtps) will be more important than the erection of entirely new plants, as most of the plants necessary in Germany already exist. Thus far, membrane bioreactor (MBR) technology is not used as an alternative for plant upgrading in Germany. However, at several locations the preconditions indicate that the application of the MBR technology for upgrading of plants may be favorable. These preconditions include the need for a substantial enlargement of the aeration tank volume and/or the need to improve the efficiency of the final sedimentation tanks, and also require that the existing tanks be in a good state, so that the tanks can be used in the future. The relevant preconditions and the basic upgrading concept using the MBR technology were presented earlier. Depending on the local preconditions regarding the existing tank volume, a specific aspect of this application can be an operation mode using “non‐conventional low MLSS (mixed liquor suspended solids) concentrations” (5 kg MLSS/m³ through 7 kg MLSS/m³) due to the amount of the existing tank volume. Two research projects were carried out covering the operation of five pilot plants on a cubic meter scale to demonstrate the feasibility of this kind of MBR process. This paper presents the core results of this research work.     

Monitoring anaerobic sequential batch reactors via fractal analysis of pH time series

Efficient monitoring and control schemes are mandatory in the current operation of biological wastewater treatment plants because they must accomplish more demanding environmental policies. This fact is of particular interest in anaerobic digestion processes where the availability of accurate, inexpensive, and suitable sensors for the on‐line monitoring of key process variables remains an open problem nowadays. In particular, this problem is more challenging when dealing with batch processes where the monitoring strategy has to be performed in finite time, which limits the application of current advanced monitoring schemes as those based in the proposal of nonlinear observers (i.e., software sensors). In this article, a fractal time series analysis of pH fluctuations in an anaerobic sequential batch reactor (AnSBR) used for the treatment of tequila vinasses is presented. Results indicated that conventional on‐line pH measurements can be correlated with off‐line determined key process variables, such as COD, VFA and biogas production via some fractality indexes. Biotechnol. Bioeng. 2013; 110: 2131–2139. © 2013 Wiley Periodicals, Inc.     

Effects of temperature, salinity, and carbon: nitrogen ratio on sequencing batch reactor treating shrimp aquaculture wastewater

In order to improve the water quality in the shrimp aquaculture, we tested a sequencing batch reactor (SBR) for the treatment of shrimp wastewater. A SBR is a variation of the activated sludge biological treatment process. This process uses multiple steps in the same tank to take the place of multiple tanks in a conventional treatment system. The SBR accomplishes pH correction, aeration, and clarification in a timed sequence, in a single reactor basin. This is achieved in a simple tank, through sequencing stages, which includes fill, react, settle, decant, and idle. The wastewater from the Waddell Mariculture Center, South Carolina was successfully treated using a SBR. The wastewater contained high concentration of carbon and nitrogen. By operating the reactor sequentially, viz, aerobic, anaerobic, and aerobic modes, nitrification and denitrification were achieved as well as removal of carbon. We optimized various environmental parameters such as temperature, salinity, and carbon and nitrogen ratio (C:N ratio) for the best performance of SBR. The results indicated that the salinity of 28-40 parts per thousand (ppt), temperature range of 22-37 degrees C, and a C:N ratio of 10:1 produced best results in terms of maximum nitrogen and carbon removal from the wastewater. The SBR system showed promising results and could be used as a viable treatment alternative in the shrimp industry.     

Biological treatment of high strength wastewater by fed-batch operation

Biological treatment systems for high strength wastewaters are usually operated in continuous mode such as activated sludge systems. When operated at steady-state, continuous systems result in constant effluent standards. However, in the presence of shock loadings and/or toxic compounds in feed wastewater, system performance drops quite significantly as a result of partial loss of microbial activity. In fed-batch operation, wastewater is fed to the aeration tank with a flow rate determined by effluent standards. In this type of operation, wastewater can be fed to biological oxidation unit intermittently or continuously with a low flow rate without any effluent removal. Feed flow rate is adjusted by measuring COD concentration in the effluent. As a result of intermittent addition of wastewater high COD concentrations and toxic compounds are diluted in large volume of aeration tank and inhibition effects of those compounds are reduced. As a result, biological oxidation of these compounds take place at a much higher rate. In order to show the aforementioned advantage of fed-batch operation, a high strength synthetic wastewater consisting of diluted molasses, urea, KH₂PO₄ and MgSO₄ was treated in an biological aeration tank by fed-batch operation. Organisms used were an active and dominant culture of Zooglea ramigera commonly encountered in activated sludge operations. COD removal kinetics was found to be first order and the rate constant was determined.     

Nitrous oxide emissions from wastewater treatment processes

Nitrous oxide (N(2)O) emissions from wastewater treatment plants vary substantially between plants, ranging from negligible to substantial (a few per cent of the total nitrogen load), probably because of different designs and operational conditions. In general, plants that achieve high levels of nitrogen removal emit less N(2)O, indicating that no compromise is required between high water quality and lower N(2)O emissions. N(2)O emissions primarily occur in aerated zones/compartments/periods owing to active stripping, and ammonia-oxidizing bacteria, rather than heterotrophic denitrifiers, are the main contributors. However, the detailed mechanisms remain to be fully elucidated, despite strong evidence suggesting that both nitrifier denitrification and the chemical breakdown of intermediates of hydroxylamine oxidation are probably involved. With increased understanding of the fundamental reactions responsible for N(2)O production in wastewater treatment systems and the conditions that stimulate their occurrence, reduction of N(2)O emissions from wastewater treatment systems through improved plant design and operation will be achieved in the near future.     

Growth monitoring of <Emphasis Type="Italic">Fibrobacter succinogenes</Emphasis> by pressure measurement

In life support systems, such as the MELiSSA (Micro-Ecological Life Support Alternative) project, developed by the European Space Agency, the aim is to understand and assemble artificial ecosystems for ensuring human subsistence in space. Fibrobacter succinogenes, an anaerobic bacterium, was used for the degradation of vegetable wastes produced in higher plants chambers, but the process does not allow the monitoring of biomass concentration and degradation rates. This study proposes a growth and a degradation monitoring technique using pressure measurements. First, volatile fatty acids (VFA) production was compared with biomass growth and with CO₂ production. The experiments were carried out in batch and fed-batch processes on glucose and on vegetables. The results have shown that a link could be established between VFA production, degradation rate and gas pressure measurements. Thus, the pressure could be used both as a relevant variable for online evaluation of biomass growth and of degradation of complex vegetable wastes.     

Methanogenesis under acidic pH conditions in a semi-continuous reactor system

Operating an anaerobic digester at low pH could offer several advantages over operation at neutral pH. Most wastewater streams targeted for anaerobic digestion are inherently acidic, requiring alkalinity supplementation (at added expense) to buffer the pH at neutral. Additionally, previously published work completed by the authors using batch systems suggested that lowering the system pH could increase methane production by as much as 30%. The goal of this research was to evaluate the feasibility of sustaining methanogenesis at low pH in a semi-continuous laboratory-scale fermentor. Significant methane production was achieved in a system ranging in pH from approximately 4.0-5.3. Results show that, if the consortium is allowed to sufficiently acclimate to acidic conditions, methanogenesis can be maintained under acidic pH conditions, resulting in overall chemical oxygen demand (COD) reduction and methane production comparable to that achieved in a neutral pH system.     

Tequila vinasses: generation and full scale treatment processes

The production of Tequila (55% Alc. Vol.) in Mexico for the year 2008 was 227 million liters, and consequently around 2,270 million liters of Tequila vinasses (TVs) were generated, which without proper treatment is equivalent to the pollution produced by 6.2 million people. The lack of both finances and technology availability are reasons for the absence of wastewater treatment plants (WTP) in the Tequila factories, with the exception of some big and medium size factories. There are WTPs based on both biological and physicochemical processes and also combinations of them that have been implemented to treat TVs; however, in most of the cases the implementation has not been effective. The WTPs that utilize a biological anaerobic process seem to be the most suitable for the treatment of TVs; however, there are some technical factors that have to be considered before the implementation of a technological solution for this environmental issue. This mini-review presents the state of the art of wastewater treatments performance in the Tequila industry, discussing the efficacy of the systems together with other technologies that could be considered to fulfill the requirements for the environmental regulation in Mexico.     

Biological treatment of ammonium-rich wastewater by partial nitritation and subsequent anaerobic ammonium oxidation (anammox) in a pilot plant

In wastewater treatment plants with anaerobic sludge digestion, 15-20% of the nitrogen load is recirculated to the main stream with the return liquors from dewatering. Separate treatment of this ammonium-rich digester supernatant would significantly reduce the nitrogen load of the activated sludge system. Some years ago, a novel biological process was discovered in which ammonium is converted to nitrogen gas under anoxic conditions with nitrite as the electron acceptor (anaerobic ammonium oxidation, anammox). Compared to conventional nitrification and denitrification, the aeration and carbon-source demand is reduced by over 50 and 100%, respectively. The combination of partial nitritation to produce nitrite in a first step and subsequent anaerobic ammonium oxidation in a second reactor was successfully tested on a pilot scale (3.6 m(3)) for over half a year. This report focuses on the feasibility of nitrogen removal from digester effluents from two different wastewater treatment plants (WWTPs) with the combined partial nitritation/anammox process. Nitritation was performed in a continuously stirred tank reactor (V=2.0 m(3)) without sludge retention. Some 58% of the ammonium in the supernatant was converted to nitrite. At 30 degrees C the maximum dilution rate D(x) was 0.85 d(-1), resulting in nitrite production of 0.35 kg NO(2)-N m(-3)(reactor) d(-1). The nitrate production was marginal. The anaerobic ammonium oxidation was carried out in a sequencing batch reactor (SBR, V=1.6 m(3)) with a nitrogen elimination rate of 2.4 kg N m(-3)(reactor) d(-1) during the nitrite-containing periods of the SBR cycle. Over 90% of the inlet nitrogen load to the anammox reactor was removed and the sludge production was negligible. The nitritation efficiency of the first reactor limited the overall maximum rate of nitrogen elimination.     

Inhibition of Biogas Production by Alkyl Benzene Sulfonates (LAS) in a Screening Test for Anaerobic Biodegradability

The effect of the inoculum source on the digestion of linear alkylbenzene sulfonates (LAS) under anaerobic conditions has been investigated. The potential for primary and ultimate LAS biodegradation of anaerobic sludge samples obtained from wastewater treatment plants (WWTPs) of different geographical locations was studied applying a batch test system. It was found that only 4–22% of the LAS added to the batch anaerobic digesters was primarily transformed suggesting a poor primary degradation of the LAS molecule in anaerobic discontinuous systems. Regarding ultimate biodegradation, the addition of LAS to the batch anaerobic digesters caused a reduction on the extent of biogas production. Significant differences in the inhibition extent of the biogas production were observed (4–26%) depending on the sludge used as inoculum. Effect of the surfactant on the anaerobic microorganisms was correlated with its concentration in the aqueous phase. Sorption of LAS on anaerobic sludge affects its toxicity by depletion of the available fraction of the surfactant. LAS content on sludge was related to the total amount of calcium and magnesium extractable ions. The presence of divalent cations promote the association of LAS with anaerobic sludge reducing its bioavailability and the extent of its inhibitory effect on the biogas production.     

State of the art of aerobic granulation in continuous flow bioreactors

In the wake of the success of aerobic granulation in sequential batch reactors (SBRs) for treating wastewater, attention is beginning to turn to continuous flow applications. This is a necessary step given the advantages of continuous flow treatment processes and the fact that the majority of full-scale wastewater treatment plants across the world are operated with aeration tanks and clarifiers in a continuous flow mode. As in SBRs, applying a selection pressure, based on differences in either settling velocity or the size of the biomass, is essential for successful granulation in continuous flow reactors (CFRs). CFRs employed for aerobic granulation come in multiple configurations, each with their own means of achieving such a selection pressure. Other factors, such as bioaugmentation and hydraulic shear force, also contribute to aerobic granulation to some extent. Besides the formation of aerobic granules, long-term stability of aerobic granules is also a critical issue to be addressed. Inorganic precipitation, special inocula, and various operational optimization strategies have been used to improve granule long-term structural integrity. Accumulated studies reviewed in this work demonstrate that aerobic granulation in CFRs is capable of removing a wide spectrum of contaminants and achieving properties generally comparable to those in SBRs. Despite the notable research progress made toward successful aerobic granulation in lab-scale CFRs, to the best of our knowledge, there are only three full-scale tests of the technique, two being seeded with anammox-supported aerobic granules and the other with conventional aerobic granules; two other process alternatives are currently in development. Application of settling- or size-based selection pressures and feast/famine conditions are especially difficult to implement to these and similar mainstream systems. Future research efforts needs to be focused on the optimization of the granule-to-floc ratio, enhancement of granule activity, improvement of long-term granule stability, and a better understanding of aerobic granulation mechanisms in CFRs, especially in full-scale applications.     

Electricity generation and treatment of paper recycling wastewater using a microbial fuel cell

Increased interest in sustainable agriculture and bio-based industries requires that we find more energy-efficient methods for treating cellulose-containing wastewaters. We examined the effectiveness of simultaneous electricity production and treatment of a paper recycling plant wastewater using microbial fuel cells. Treatment efficiency was limited by wastewater conductivity. When a 50 mM phosphate buffer solution (PBS, 5.9 mS/cm) was added to the wastewater, power densities reached 501 +/- 20 mW/m(2), with a coulombic efficiency of 16 +/- 2%. There was efficient removal of soluble organic matter, with 73 +/- 1% removed based on soluble chemical oxygen demand (SCOD) and only slightly greater total removal (76 +/- 4%) based on total COD (TCOD) over a 500-h batch cycle. Cellulose was nearly completely removed (96 +/- 1%) during treatment. Further increasing the conductivity (100 mM PBS) increased power to 672 +/- 27 mW/m(2). In contrast, only 144 +/- 7 mW/m(2) was produced using an unamended wastewater (0.8 mS/cm) with TCOD, SCOD, and cellulose removals of 29 +/- 1%, 51 +/- 2%, and 16 +/- 1% (350-h batch cycle). These results demonstrate limitations to treatment efficiencies with actual wastewaters caused by solution conductivity compared to laboratory experiments under more optimal conditions.     

Implementing a composite indicator approach for prioritizing activated sludge-based wastewater treatment plants at large spatial scale

Successful implementation of the European Urban Wastewater Treatment Directive requires a deepened and multidisciplinary knowledge of the wastewater systems. The development of ready-to-use tools for decision makers is, in this sense, a challenge. This paper proposes a methodology to efficiently prioritize wastewater treatment plants (WWTPs) on the basis of the relative environmental, social and public health impacts, taking into account the territorial context issues. The proposed methodology has led to the implementation of a composite indicator. The several choices made for its development, from the definition of framework to the final outcomes, have been evaluated in depth and are supported through methodological and statistical techniques. The potential use of the composite indicator with the inherent advantages and limitations are discussed in order to provide a ready-to-use tool for final users for WWTPs prioritization. Moreover, a concise methodology for composite index implementation is described.