Ice-cream Wastewater Research Articles

Activated carbon from hydrothermal carbonization of ice cream factory wastewater with H3PO4 activation. Synthesis, characterisation and adsorption properties

This work aims to treat ice cream wastewater (ICWW) by hydrothermal carbonization (HTC) and to produce activated carbon (AC). The HTC reduces COD, BOD5 and KTN by up to 80%, 55% and 93%, respectively. The obtained hydrochar was activated with H3PO4 at various impregnation ratios (1−4) and different temperatures (400−600 °C). The material with the best properties, named AC-2-500, was obtained at 500 °C with an acid impregnation rate of 2 and represents a spherical shape (specific surface area of 1432.44 m2 g−1, pore volume of 0.80 cm3g-1, and average pore diameter around 2.24 nm). The porous structure of AC-2-500 enabled to achieve high adsorption capacities of the order of 588.23 mg g−1 and 250 mg g−1 for rhodamine B (RhB) and acid red 97 (AR97), respectively. The adsorption equilibrium was reached in 30 min for RhB and 60 min for AR97. The linear forms of the Langmuir and Freundlich isotherms appear to produce reasonable models for the adsorption of dyes onto AC-2-500, with best results when applying Langmuir model. Both dyes adsorb spontaneously and endothermically, with an increase in the randomness at the solid/solution interface. Furthermore, the regeneration study revealed that during several adsorption-desorption cycles, AC-2-500 demonstrated a strong adsorption capability.

Microalgal-bacterial treatment of ice-cream wastewater to remove organic waste and harvest oil-rich biomass.

The diversity of microalgae and bacteria allows them to form beneficial consortia for efficient wastewater treatment and nutrient recovery. This study aimed to evaluate the feasibility of a new microalgal-bacterial combination in the treatment of ice cream wastewater for biomass harvest. The bacterium Novosphingobium sp. ICW1 was natively isolated from icecream wastewater and the microalga Vischeria sp. WL1 was a terrestrial oil-producing strain of Eustigmatophyceae. The ice cream wastewater was diluted 4 folds for co-cultivation, which was relatively less inhibitory for the growth of Vischeria sp. WL1. Four initial algal-bacterial combinations (v:v) of 150:0 (single algal cultivation), 150:1, 150:2, and 150:4 were assessed. During 24days of co-cultivation, algal pigmentation was dynamically changed, particularly at the algal-bacterial combination of 150:4. Algal growth (in terms of cell number) was slightly promoted during the late phase of co-cultivation at the combinations of 150:2 and 150:4, while in the former the cellular oil yield was obviously elevated. Treated by these algal-bacterial combinations, total carbon was reduced by 67.5 ~ 74.5% and chemical oxygen demand was reduced by 55.0 ~ 60.4%. Although single bacterial treatment was still effective for removing organic nutrients, the removal efficiency was obviously enhanced at the algal-bacterial combination of 150:4. In addition, the harvested oils contained 87.1 ~ 88.3% monounsaturated fatty acids. In general, this study enriches the biotechnological solutions for the sustainable treatment of organic matter-rich food wastewater.

Kinetic Modeling of Amino Acid Production from Ice-Cream Wastewater in Subcritical Conditions

Wastewater derived from ice-cream manufacture contains high concentration of protein, making it a suitable feedstock for hydrolysis. In this study, ice-cream wastewater was hydrolyzed under subcritical conditions (170–230 °C and 40 bars) and different nominal pH (3, 6, and 9) to produce amino acids. The formation and subsequent degradation of amino acids were modeled using a two-consecutive reaction model. Apparent activation energy for the formation and degradation of amino acids varied from 41 to 83 and 33 to 59 kJ/mol, respectively, changing with the nominal pH. The amino acid profile showed 21 amino acids, whose concentration was strongly influenced by the reaction conditions. The maximum concentration of amino acids was found within the first 50 min at 170 °C and nominal pH 3. After 50 min, a mixture of amino acids was obtained mainly made of glutamic acid (20–30%), proline (9–12%), aspartic (3–10%), and leucine (9–12%), showing slight variation with the nominal pH. Subcritical hydrolysis of ice-cream wastewater showed to be an effective alternative to produce amino acids that can be used as platform chemicals.

Subcritical hydrolysis of ice-cream wastewater: Modeling and functional properties of hydrolysate

The hydrolysis kinetics of ice-cream wastewater was studied under subcritical conditions (130–230°C and 20–60bar) in a continuous stirred-tank reactor. The kinetic was monitored by measuring the degree of hydrolysis (DH, %) at different time intervals (up to 240min). Samples of ice-cream wastewater were collected from the university dairy plant after a typical clean-in-place protocol. Overall, the reaction time and temperature significantly increased the DH, reaching a maximum value of 40.99±0.81, 34.44±0.47, 20.61±0.42, and 5.74±0.36% after 200–240min at 130, 170, 200 and 230°C, respectively. The experimental data were modeled using the Weibull distribution model showing a satisfactory correlation between experimental data and predicted values (R2=0.971). The apparent activation energy for subcritical hydrolysis was 37.53±5.21kJmol−1. After 240min of reaction, the hydrolyzates were recovered, and their antiradical ability was measured through free radical scavenging (2,2-diphenyl-1-picrylhydrazyl) method. Additionally, the angiotensin converting enzyme (ACE)-inhibitory ability was determined. The inhibition of a free radical was found to increase linearly with the DH (R2=0.991). The hydrolysate recovered at 230°C showed the highest ACE-inhibitory ability (98.0±1.6%). The study outcomes present an opportunity for utilizing subcritical hydrolysis to convert wastewater into valuable materials.

Investigation on Fluidized Bed Bioreactor Treating Ice Cream Wastewater Using Response Surface Methodology and Artificial Neural Network

Abstract In this study, a comparative approach was developed between response surface methodology (RSM) and artificial neural network (ANN) in the predictive capabilities for the removal of chemical oxygen demand (COD) from ice cream industry wastewater using fluidized bed bioreactor. The effects of process variables such as pH, temperature, flow rate and agitation speed investigated using a four-factor three-level Box–Behnken experimental design (BBD). Same design was utilized to train a feed-forward multilayered perceptron (MLP) ANN with back-propagation algorithm. The predictive capabilities of the two methodologies were compared in terms of statistical parameters including coefficient of determination (R2). The results showed that properly trained ANN model is more accurate in prediction as compared to RSM model. Under the optimum conditions (pH of 7, temperature of 40°C, flow rate of 20 ml/min and agitation speed of 175 rpm), 91% of COD was removed.

Recovery of biogas as a source of renewable energy from ice-cream production residues and wastewater

Proper management of waste streams and residues from agro-industry is very important to prevent environmental pollution. In particular, the anaerobic co-digestion process can be used as an important tool for safe disposal and energy recovery from agro-industry waste streams and residues. The primary objective of this laboratory-scale study was to determine whether it was possible to recover energy (biogas) from ice-cream production residues and wastewater, through a mesophilic anaerobic co-digestion process. A high methane yield of 0.338 L CH4/g CODremoved could be achieved from anaerobic digestion of ice-cream wastewater alone, with almost 70% of methane in biogas, while anaerobic digestion of ice-cream production residue alone did not seem feasible. When wastewater and ice-cream production residue were anaerobically co-digested at a ratio of 9:1 by weight, the highest methane yield of 0.131 L CH4/gCODremoved was observed. Buffering capacity seemed to be imperative in energy recovery from these substrates in the anaerobic digestion process.

A fundamental analysis of continuous flow bioreactor models governed by Contois kinetics. II. Reactor cascades

Abstract The rate determining step of a number of biological processes is now known to be described by Contois growth kinetics. In particular this growth rate has been found to describe the treatment of contaminated wastewaters containing biodegradable organic materials from a variety of industrial processes. The efficient treatment of such waste materials is of ever growing environmental concern. This contribution is the first steady-state analysis for the treatment of industrial wastewaters, obeying Contois kinetics, in a cascade of continuous flow bioreactors without recycle. The steady-states of the model are found and their stability determined as a function of the residence time in each reactor of the cascade. Asymptotic solutions are obtained for the effluent concentration leaving a cascade of n reactors for two scenarios, in which it is assumed that the reactors in the cascade have the same residence time. In the first scenario the limiting case of large total residence time ( τ t ∗ ) is considered. The effluent concentration leaving the reactor ( S n ∗ ) is found to be given by S n ∗ ≈ ( 1 / τ ∗ n ) , when n = 1 , 2 , 3 and 4. It is conjectured that this relationship holds for all n. Thus, for a fixed total residence time increasing the number of reactors in the the cascade has a dramatic effect on the quality of the wastewater leaving the cascade. In the second scenario, the limiting case when the total residence time is slightly larger than the washout point is considered. In this region, a small increase in the total residence time leads to a large decrease in the effluent concentration. These results are illustrated by considering the anaerobic digestion of ice-cream wastewater.

Improved split feed anaerobic baffled reactor (SFABR) for shorter start-up period and higher process performance

In this paper, the Split Feed Anaerobic Baffled Reactor (SFABR) is introduced and investigations into the use of modified seed material are described. It was shown that shorter and reliable start-up times could be achieved with SFABR when using improved seed material, even for the treatment of particularly problematic wastewater, i.e. ice-cream wastewater. Scanning electron photo-micrographs (SEM) revealed that granulation process occurs relatively rapidly in the SFABR compared with other reactor configurations, and that the reactor contained a highly mixed population of methanogens in all compartments. The use of polymer-conditioned anaerobic sludge and granular sludge as seed proved advantageous over the use of suspended growth anaerobic sludge, and the "improved" SFABR consequently performed more efficiently and also showed greater stability than the conventional ABR.

The effect of polymer addition on granulation in an anaerobic baffled reactor (ABR). Part I: process performance

The stability and performance of an anaerobic baffled reactor (ABR) treating an ice-cream wastewater at several organic loading rates have been investigated. Specifically, it was determined whether an ABR would promote phase separation and if a polymer additive was capable of enhancing granule formation in an ABR. In order to achieve these goals, two ABRs, having identical dimensions and configurations, were used to study the above objectives using a synthetic ice-cream wastewater. The ABR proved to be an efficient reactor configuration for the treatment of a high-strength synthetic ice-cream wastewater. An organic loading rate of around 15 kg COD m −3 d −1 was treated with a 99% COD removal efficiency. From the jar test and inhibition assay, it was concluded that Kymene SLX-2 was the most effective and least inhibitory polymer tested. The methane yield was higher in the polymer-amended reactor compared to the control reactor. In addition, polymer addition resulted in a considerably higher degree of biomass retention and lower solids washout from the ABR. Consequently, it demonstrated that there was a considerable potential for sludge conditioning in ABRs by facilitating better biomass retention within the reactor which in turn led to better process performance. Granulation was achieved in both ABRs within 3 months. However, the granules from the polymer-amended reactor appeared earlier and were generally larger and more compact, although this was not quantified in detail during the present study. The main advantage of using an ABR comes from its compartmentalised structure. The first compartment of an ABR may act as a buffer zone to all toxic and inhibitory material in the feed thus allowing the later compartments to be loaded with a relatively harmless, balanced and mostly acidified influent. In this respect, the latter compartments would be more likely to support active populations of the relatively sensitive methanogenic bacteria and partly explains why the best granules and the highest methane yield were obtained in Compartment 2. It is unlikely that a complete separation of phases (acidogenic and methanogenic) occurred within the ABRs since methane production was observed in all compartments, although this was low (∼40% of all gas composition) in Compartment 1, becoming higher (∼70%) in the following compartments.

The effect of polymer addition on granulation in an anaerobic baffled reactor (ABR). Part II:: compartmentalization of bacterial populations

The microbial ecology of wastewater treatment plants remains one of the least understood aspects in both aerobic and anaerobic systems, despite the fact that both processes are ultimately dependent on an active biomass for operational efficiency. Ultimately, future developments in anaerobic treatment processes will require a much greater understanding of the fundamental relationships between bacterial populations within the biomass if optimum process efficiency is to be fully realised. This study assesses the influence of polymer addition on granule formation within an ABR and compares the ecology of the biomass in each compartment of two ABRs treating ice-cream wastewater. To our knowledge, this is the first reported characterisation of the microbiology of acidogenic and methanogenic bacteria in the individual compartments of an ABR. The polymer-amended reactor contained sludge that had a greater density of anaerobic bacteria and larger and denser granules than the control reactor, indicating that polymer addition possibly contributed to the retention of active biomass within the ABR. The average fraction of autofluorescent methanogens was lower, with 1.5% being in the initial compartments of the ABRs, compared to the last compartment which had 15%, showing that each compartment of an ABR had a unique microbial composition. Partial spatial separation of anaerobic bacteria appeared to have taken place with acidogenic bacteria predominating in the initial compartments and methanogenic bacteria predominating in the final compartments. Scanning electron micrographs have revealed that the dominant bacteria in the initial compartments of the ABR (Compartments 1 and 2) were those which could consume H 2/CO 2 and formate as substrate, i.e. Methanobrevibacter, Methanococcus, with populations shifting to acetate utilisers, i.e. Methanosaeta, Methanosarcina, in the final compartments (Compartments 3 and 4). In addition, there appeared to be a stratified structure to the bacterial genera present within the granules.

A kinetic study of the anaerobic digestion of ice-cream wastewater

The process kinetics of the mesophilic (35 °C) anaerobic digestion of ice-cream wastewater was investigated. The Monod equation and the Contois equation were used to develop two basic steady-state models. The kinetic parameters required for the application for the steady-state models were determined using a laboratory-scale continuously stirred tank reactor (5 l) fed with a synthetic ice-cream wastewater at a range of hydraulic retention times (2.99–7.45 days). Both models were evaluated with a set of routine analytical data obtained from a pilot-scale (5 m 3) anaerobic contact digester treating the ice-cream wastewater at a commercial site. The steady-state model obtained with the Contois equation was more suitable than that obtained with the Monod equation for describing the process kinetics of the pilot-scale anaerobic contact process. The main reason for this is that the kinetic model based on the Contois equation considers the effect of any changes in influent substrate concentration in its prediction.

Response of an anaerobic fluidized bed reactor treating ice-cream wastewater to organic, hydraulic, temperature and pH shocks

An anaerobic fluidized bed reactor, operating at 35° C, was used to treat ice-cream wastewater with an influent chemical oxygen demand (COD) of 5.2 g l −1. Start-up of the reactor was achieved within 30 days by use of a regime that included stepped increases in influent COD and methanol substitution of the substrate. A steady state was achieved with 94.4% COD reduction at an organic COD loading rate of 15.6 g l −1 d −1 (HRT 8 h). This rate is somewhat faster than those achieved in previously reported studies. The reactor was subjected to transient changes in temperature, pH, influent flow-rate and COD for 6 and 12 h periods. The quality of the effluent deteriorated under these shock load conditions but returned to steady-state values within 6–16 h upon restoring normal conditions. The stability of the reactor under unfavourable process conditions is discussed.

Anaerobic digestion of ice-cream wastewater: A comparison of single and two-phase reactor systems

The anaerobic digestion of ice-cream wastewater, a complex substrate which includes milk proteins, carbohydrates, and lipids, has received little attention. Work using an aerobic contact system showed that at a 7.5-d hydraulic retention time (HRT), with an organic loading rate of 1.7 g COD/Ld and influent TSS (total suspended solids) of 5870 mg/L, the effluent COD was 628 mg/L, BOD was 91 mg/L and TSS was 674. Anaerobic filters have also been used at organic loadings of 6 kg COD/m{sup 3}d applied at a HRT of 0.42 day, with COD removals of 80%. Goodwing showed that this waste was capable of being treated by the UASB process with granulation commencing after 60-70 days, and gas production ranging between 0.73 and 0.93 L CH{sub 4}/g COD removed with loading rates between 0.7 and 3.0 g TOC/Ld. Two-phase anaerobic digestion is an innovative fermentation mode that has recently received increased attention. The kinetically dissimilar fermentation phases, hydrolysis-acidification and acetogenesis-methanation are operated in two separate reactors; the first of which is maintained at a very short HRT. The effluent from the first, acid-forming, phase is used as the substrate for the methane-phase reactor which has a longer HRT or cell immobilization. The aimmore » of this work was to compare the methane production capability and performance of a single-phase upflow fixed bed reactor with a two-phase digestion system. The two-phase digestion system consists of a completely mixed reactor for the acidogenic reaction and an upflow fixed bed reactor for the methanogenic reaction. Because of the high lipid content and COD of ice cream wastewater off site disposal has proved to be both expensive and poses problems to the receiving effluent treatment plant. For this reason the potential for a rapid anaerobic stabilization of the waste, with energy recovery in the form of methane gas, has been investigated in an attempt to minimize plant size and maximize gas production. 9 refs., 2 tabs.« less

Comparative performance of anaerobic digesters operating on ice-cream wastewater

Pilot-scale anaerobic digesters were operated on ice-cream wastewater for over three years. The performance of four reactor designs, an anaerobic filter, contact process and UASB of capacity 5 m 3, and a 0.5 m 3 fluidised bed, was compared. The anaerobic filter, with a 3.3 m 3 Pall ring bed, operated stably at organic loading rates ( B v) around 6 kg COD m −3d −1, giving total COD removals around 67%. The contact process gave consistently good total COD removals of 80%, but was limited by the poor performance of the settling compartment. Mixed liquor suspended solids did not rise above 3 kg m −3, and this reactor operated at B v of 1 kg COD m −3d −1. The fluidised bed reactor, operated on sand or granular activated carbon support media at B v of 4 and 2 kg COD m −3d −1 respectively, gave about 60% total COD removal, but difficulty was experienced with GAC break-up. The UASB reactor gave the poorest performance, (approximately 50% total COD removal at a B v of 2 kg COD m −3d −1) since successful granulation was not achieved. The anaerobic filter was also operated for 9 months after removing half of its packing material, but the former loading rate could not be achieved without instability. Poor biomass retention in all reactors, possibly related to the fat content of the wastewater, was the limiting factor in performance. Using experience gained at pilot scale, a full-scale upflow anaerobic filter was subsequently installed on an ice-cream factory site. This reactor showed similar performance to the pilot-scale filter.

On-line monitoring of anaerobic digestion: application of a device for continuous measurement of bicarbonate alkalinity

Alkalinity or pH buffering capacity in anaerobic digesters is chiefly a function of bicarbonate levels, and should be within 10 to 50 mM for stable operation. A novel on-line instrument for measuring bicarbonate alkalinity has been developed, independent of titration techniques. Using a 10 litre anaerobic filter digester operating on ice-cream wastewater, on-line measurements were made of bicarbonate alkalinity, pH, gas production and % CO2 and hydrogen concentration in the biogas during periods of organic overload. The bicarbonate alkalinity monitor was shown to be an effective instrument for monitoring instability of anaerobic digestion, and a useful tool for early warning of overloading. Moreover, in digesters fed with wastewaters containing low potential alkalinity, it allows indirect on-line determination of variations in volatile fatty acid concentration. Finally, used in conjunction with a sensor that measures CO2 in the gas, it allows an indirect but accurate determination of pH in those solutions where fouling of electrodes is severe.

The Stability of Anaerobic Digesters Operating on a Food-Processing Wastewater

The response to step overloads of laboratory-scale contact process and UASB reactors and a pilot-scale anaerobic filter is examined. The reactors were operated on ice-cream waste water and changes in operational parameters including VFA levels and COD reduction were monitored. In the laboratory-scale experiments, feed strength was increased from 4500 to 22,000 mg [O] per litre for periods of 2 to 12 hours in contact process and one and two-stage UASB reactors. UASB stability was improved by supplementing with trace metals. Two-stage UASB's gave better COD removals under shock loading than single-stage UASB's or contact process reactors. In an 8 hour step overload experiment on the pilot-scale reactor, bicarbonate alkalinity was shown to be a good indicator of instability.

Changes to the microbial ecology in anaerobic digesters treating ice cream wastewater during start-up

Changes to the microbial ecology in four different designs of pilot-scale, high rate anaerobic reactor, treating a synthetic ice cream waste, were studied during the initial start-up phase. The nature of the biomass and the numbers of non-methanogenic and methanogenic bacteria remained similar in all the digesters. Variations within the bacterial populations did occur but statistical analysis showed no significant difference between the numbers in each reactor and with respect to time after start-up. Within the fluorescent methanogen population, selection of an organism tentatively identified as either Methanobacterium formicicium or a species of Methanobrevibacter occurred. Reactor design did not appear to be as important as the wastewater composition in causing changes to the microbial communities. The problems of using conventional microbial enumeration methods in the study of complex microbial communities such as digester sludge are also discussed.

Anaerobic digestion of ice-cream wastewaters using the UASB process

A set of ten upflow sludge blanket digesters was examined as five pairs (one control and four test reactors) to assess the way in which controlled nutrient variations affected the performance of the reactors in treating a simulated ice-cream wastewater. An alternative carbon source was used and additional concentrations of calcium and cobalt were examined. The results show that the waste itself is capable of being treated by the UASB process, with granulation commencing after 60–70 days. However, of the supplements, only calcium had any significant effect.