Dissolved Air Flotation Sludge Research Articles

Dissolved Air Flotation: A Review from the Perspective of System Parameters and Uses in Wastewater Treatment

The current issues of climate change and high freshwater demand worldwide have promoted the implementation of wastewater reclamation technologies. This study aims to review the efficiency of the dissolved air flotation (DAF) technique in a wide variety of applications in the agricultural, industrial, domestic, and municipal sectors, which have high freshwater consumption worldwide. We made a systematic review of the DAF technique in wastewater treatment in 2015-2021. We reviewed six indexed databases and governmental statistical reports; we used the keywords: dissolved air flotation, microbubbles, wastewater treatment, and the main operating and design parameters involved in the effectiveness of the flotation process. Additionally, we conducted a review of the most common synthetic coagulant studies used with DAF, as well as natural coagulants that promise to mitigate current climate change. Finally, we discussed advantages, disadvantages, and potential future studies. DAF to have considerable potential for wastewater treatment, as well as for waste utilization. The generation of large quantities of DAF sludge is a breakthrough for clean energy production, as it allows the use of this waste for biogas production.

Chocolate industry side streams as a valuable feedstock for microbial long-chain dicarboxylic acid production

Two high-fat containing side streams from the chocolate industry were evaluated as an alternative renewable substrate for biochemical long-chain dicarboxylic acid (DCA) production by Candida tropicalis. Cleaning water from liquid chocolate transport and dissolved air flotation (DAF) sludge from the wastewater treatment plant contained 29 and 18 m% fat respectively. The addition of up to 100 g.L−1 of the ‘chocolate water’ and 80 % (v/v) of DAF sludge had no negative effects on both growth and DCA production. In a fed-batch reactor, a DCA concentration of 5.8 g.L−1 was obtained after 120 h and 47.5 % of the consumed fats were converted to DCA upon glucose addition when using chocolate water. Using DAF sludge, a DCA concentration of 4.9 g.L−1 was obtained after 72 h, equalling 37.5 % of the consumed fats. This research shows the potential of the researched side streams as a substrate for DCA production.

Prognostic Assessment of the Viability of Hydrothermal Liquefaction as a Post-Resource Recovery Step after Enhanced Biomethane Generation Using Co-Digestion Technologies

In line with global efforts at encouraging paradigm transitions from waste disposal to resource recovery, the anaerobic co-digestion of substrates of wet hydrolyzed meat processing dissolved air flotation sludge and meat processing stock yard waste was investigated in the present study. It was demonstrated that the co-digestion of these substrates leads to the introduction of co-digestion synergizing effects. This study assessed biomethane potentials of the co-digestion of different substrate mixtures, with the preferred substrate mixture composed of stockyard waste and wet hydrolyzed meat processing dissolved air flotation sludge, present in a 4:1 ratio on a volatile solid mass basis. This co-digestion substrate mix ratio presented an experimentally determined cumulative biomethane potential of 264.13 mL/gVSadded (volatile solid). The experimentally determined cumulative biomethane potential was greater than the predicted maximum cumulative biomethane potential of 148.4 mL/gVSadded, anticipated from a similar substrate mixture if synergizing effects were non-existent. The viability of integrating a downstream hydrothermal liquefaction processing of the digestate residue from the co-digestion process, for enhanced resource recovery, was also initially assessed. Assessments were undertaken via the theoretical based estimation of the yields of useful products of biocrude and biochar obtainable from the hydrothermal liquefaction processing of the digestate residue. The environmental sustainability of the proposed integrated system of anaerobic digestion and hydrothermal liquefaction technologies was also initially assessed. The opportunity for secondary resource recovery from the digestate, via the employment of the hydrothermal liquefaction process and the dependence of the environmental sustainability of the integrated system on the moisture content of the digestate, were established. It is anticipated that the results of this study will constitute an invaluable basis for the future large-scale implementation of the proposed integrated system for enhanced value extraction from organic waste streams.

Scaled-Up Biodiesel Production from Meat Processing Dissolved Air Flotation Sludge: A Simulation Study

For the first time, a steady state computational simulation for the production of biodiesel from meat processing dissolved air flotation sludge via an integrated process of in-situ hydrolysis and esterification technologies has been investigated. Important thermophysical properties of the intrinsic lipids of dissolved air flotation sludge were estimated using chemical constituent fragment methods. The environmental performance and the economic performance of the biodiesel production process were assessed via the estimation of the net energy ratio (NER) and the unit production cost, respectively. Since electrical energy requirements may be satisfied via either non-renewable (case A) or renewable sources (case B), the NER was determined for both scenarios. To enhance the robustness of the study results, uncertainties in the NER and the unit cost of the biodiesel production process due to the variability of the underlying study assumptions were also assessed. Uncertainty analysis indicated that the likely range of the NER for the biodiesel production process for cases A and B are 1.76 to 3.32 and 1.82 to 3.36, respectively, at 95% probability. Uncertainty analysis also showed that the likely range of the unit production cost for biodiesel is $US0.41/kg-biodiesel to $US0.71/kg-biodiesel at 95% probability. The results that were obtained in this study therefore provide evidence of both the environmental sustainability and the economic viability of biodiesel production from dissolved air flotation sludge via the proposed integrated process of in-situ hydrolysis and esterification.

Impact of thermobaric pre-treatment on the continuous anaerobic digestion of high-fat cattle slaughterhouse waste

Thermobaric pre-treatment of a combination of dissolved air flotation (DAF) sludge and slaughterhouse wastewater was evaluated for performance over 50 days of continuous anaerobic digestion. Continuous digestion was conducted over three phases represented by varying fat, oils and grease (FOG) concentrations and organic loading. In comparison with earlier biochemical methane potential (BMP) investigations using thermobaric treated substrate by Harris, Schmidt and McCabe (Harris et al., 2017) which yielded an 8.32% increase in specific methane production, pre-treated DAF sludge produced negative impacts on digestion under continuous conditions. Average pH was consistently lower by 0.04, and loss of volatile organics during pre-treatment reduced methane yield by 12.1%. H2S concentration was 56% higher on average with 795 ppm compared with 510 ppm in the controls owing to enhanced protein degradation. Alkalinity was low due to insufficient replacement from the substrate. Fresh substrate containing double the fat content (236 mg/L) and reduced organic loading rate (OLR) caused both control and treatment reactors to fail, highlighting the need for consistent substrate characteristics. Magnesium hydroxide addition effectively recovered both pH and biogas production within digesters rapidly, addressing the underlying complication of insufficient alkalinity contribution by the substrate.

Meat processing dissolved air flotation sludge as a potential biodiesel feedstock in New Zealand: A predictive analysis of the biodiesel product properties

This paper examines the potential of utilising dissolved air flotation sludge obtained from a local meat processing plant in New Zealand as a viable biodiesel feedstock. In this study the dissolved air flotation sludge was characterised and the physicochemical properties of the lipid extract were assessed. The fatty acids present in the lipid extract were explored as a precursor to the estimation of the fuel properties of the biodiesel produced. This study has demonstrated the insufficiency of the traditional alkaline catalysed transesterification biodiesel pathway when meat processing dissolved air flotation sludge is utilised as a biodiesel feedstock. Therefore an alternative integrated hydrolysis and esterification production process has been proposed. The fluid behaviour (Newtonian or non-Newtonian) of the lipid extract was investigated to facilitate an improved understanding of the nature and physical state of the extract. Using a thermodynamic model and experimental data from the literature, the fuel properties, viscosity, density, oxidative stability, heating value and cetane number, of the produced biodiesel as a function of the fatty acid methyl ester profile were estimated. These properties satisfy the existing biodiesel fuel property standards. A preliminary economic assessment of the biodiesel production process using the dissolved air flotation sludge as the feedstock was also conducted. The initial favourable financial results provided a compelling basis for further investigations into the techno-economic feasibility of the production process. The poor cold flow properties of the produced biodiesel were however identified as significant considerations that may limit the utilisation of the dissolved air flotation sludge as a biodiesel feedstock in a temperate climate region like New Zealand. Possible solutions to this problem were initially discussed. In addition, health and safety concerns with the utilisation of this feedstock were identified. Approaches to limit the harmful effects of possible pathogenic content and unpleasant smell of this feedstock were also explored.

Waste management in the meat processing industry: Conversion of paunch and DAF sludge into solid fuel

This article addresses the novel dewatering process of immersion-frying of paunch and dissolved air flotation (DAF) sludge to produce high energy pellets. Literature have been analysed to address the feasibility of replacing conventional boiler fuel at meat processing facilities with high energy paunch-DAF sludge pellets (capsules). The value proposition of pelleting and frying this mixture into energy pellets is based on a Cost-Benefit Analysis (CBA). The CBA is based on information derived from the literature and consultation with the Australian Meat Processing Industry.The calorific properties of a mixture of paunch cake solids and DAF sludge were predicted from literature and industry consultation to validate the product. This study shows that the concept of pelletizing and frying paunch is economically feasible. The complete frying and dewatering of the paunch and DAF sludge mixture produces pellets with energy content per kilogram equivalent to coal. The estimated cost of this new product is half the price of coal and the payback period is estimated to be between 1.8 and 3.2years. Further research is required for proof of concept, and to identify the technical challenges associated with integrating this technology into existing meat processing plants.

Modelling methane production kinetics of complex poultry slaughterhouse wastes using sigmoidal growth functions

The kinetic evaluation of the methane potential from poultry slaughterhouse waste streams was performed using modified sigmoidal bacterial growth curve equations (Richards, logistic, Gompertz) in order to investigate their suitability to describe the degradation patterns associated with complex substrates, primarily composed of fats. The methane potential and degradation patterns under mesophilic conditions were assessed using Biochemical Methane Potential (BMP) assays. A nonlinear least-square regression analysis was performed to fit the sigmoidal functions to the cumulative methane production curves with respect to time generated from the BMP assays. In the cases modelled the Gompertz and logistic, three parameter models, sufficiently described the methane generation of the simple substrates (dissolved air flotation sludge) with no sign of acute inhibition due to high fat contents. When dealing with more complex degradation patterns of the substrates with a higher fat content (soft offals) and increased bioavailability of the organics, the three parameter models became insufficient in describing the experimental data due to features of the original growth functions, in particularly their fixed points of inflection. In such cases the fourth parameter afforded in the Richards model became critical allowing variability in the point of inflection allowing a much better fit to the experimental curves.

Biogas from cattle slaughterhouse waste: Energy recovery towards an energy self-sufficient industry in Ireland

This study was carried out to assess the energy recovery potential from organic industrial by-products of a cattle slaughtering facility. There are several processes to convert organic material to energy; the technology of interest in this study was anaerobic digestion, the biological conversion of degradable organic material into methane. The scenario was initially confined to a full scale cattle slaughtering facility processing 3.28% of heads slaughtered in Ireland. The methane potential of dissolved air flotation sludge, paunch, soft offal as well as a mixed waste stream (combination of individual waste streams) was determined through a series of biochemical methane potential assays under mesophilic conditions. The methane potential of the characterised waste streams ranged from 49.5 to 650.9 mLCH4 gVS−1. The potential energy recovery from the mixed waste stream resulted in the prospective subsidy of 100% of the energy demands of the slaughtering facility as well as the energy demands for the production of the biogas. When investigating the impact of energy recovery from the entire sector the potential energy recovery equated to 1.63% of the final energy demands of the Irish industrial sector. This could potentially increase the RES in Ireland from 7.8% to 8.13% contributing to both RES-E and RES-H.

Fat recovery from dissolved air flotation sludge

Fat recovery from dissolved air flotation sludge

Effect of ultrasound and addition of bacterial product on hydrolysis of by-products from the meat-processing industry

The hydrolysis efficiency of ultrasound (US) and bacterial product (BP; Liquid Certizyme 5™) was studied as a pre-treatment for anaerobic digestion (AD) of four animal by-products (ABP) from the meat-processing industry (digestive tract content + drumsieve waste, dissolved air flotation (DAF) sludge, grease trap sludge and the mixture of these). The change in volatile solids (VS) based hydrolysis parameters was screened using different specific US energy (Es) inputs (1000–14,000 kJ/kg of total solids (TS)) and durations of BP treatment (3–48 h). The Es of 6000–8500 kJ/kg TS increased most extensively the soluble chemical oxygen demand (CODsol) and VS ratio, by 45–290%, and soluble nitrogen (Nsol) by 44–99%. Simultaneously, the average particle size (APS) decreased by 45–75%, from the original value. With BP, the highest increases in CODsol/VS (29–130%), Nsol (35–63%) and decline in APS (40–70%) depended on the raw material (digestive tract content + drumsieve waste: 3 and 24 h; DAF sludge: 3 and 6 h, mixture: 12 and 48 h). BP apparently was more effective at hydrolyzing smaller cellulose particles, while US appeared to enhance the degradation of grease-containing cells.

Stable thermophilic anaerobic digestion of dissolved air flotation (DAF) sludge by co-digestion with swine manure

Environmentally sound treatment of by-products in a value-adding process is an ongoing challenge in animal agriculture. The sludge produced as a result of the dissolved air flotation (DAF) wastewater treatment process in swine processing facilities is one such low-value residue. The objective of this study was to determine the fundamental performance parameters for thermophilic anaerobic digestion of DAF sludge. Testing in a semi-continuous stirred tank reactor and in batch reactors was conducted to determine the kinetics of degradation and biogas yield. Stable operation could not be achieved using pure DAF sludge as a substrate, possibly due to inhibition by long-chain fatty acids or to nutrient deficiencies. However, in a 1:1 ratio (w/w, dry basis) with swine manure, operation was both stable and productive. In the semi-continuous stirred reactor at 54.5 °C, a hydraulic residence time of 10 days, and an organic loading rate of 4.68 gVS/day/L, the methane production rate was 2.19 L/L/day and the specific methane production rate was 0.47 L/gVS (fed). Maximum specific methanogenic activity (SMA) in batch testing was 0.15 mmoles CH 4 h −1 gVS −1 at a substrate concentration of 6.9 gVS L −1. Higher substrate concentrations cause an initial lag in methane production, possibly due to long-chain fatty acid or nitrogen inhibition.

Effect of pre-treatments on hydrolysis and methane production potentials of by-products from meat-processing industry

In this study, the effect of five pre-treatments (thermal, ultrasound, acid, base and bacterial product) on hydrolysis and methane production potentials of four by-products from meat-processing industry was studied. The bacterial product Liquid Certizyme 5™ increased soluble chemical oxygen demand (CODsol) of digestive tract content and drumsieve waste the most as compared to untreated material (62 and 96%, respectively), while ultrasound was the most effective to increase CODsol with dissolved air flotation (DAF) sludge (88%) and grease trap sludge (188%). In batch experiments, thermal treatment increased methane production potential of drumsieve waste, acid of grease trap sludge and all pre-treatments of DAF sludge. However, with all other pre-treatments, methane production potential was decreased compared to untreated materials, apparently due to inhibition by hydrolysis products and/or possible re-crystallization of some compounds. Methane production potentials from the untreated materials were as follows: digestive tract content 400 ± 50 m 3 CH 4/t volatile solids (VS) added, drumsieve waste 230 ± 20 m 3 CH 4/tVS added, DAF sludge 340 ± 17 m 3 CH 4/tVS added and grease trap sludge 900 ± 44 m 3 CH 4/tVS added.

Application of the flotation process to thicken the sludge from a DAF plant

Dissolved air flotation (DAF) was evaluated for thickening of the sludges from a water treatment plant which uses DAF. Solid flux theory for gravity thickening was applied to the solid flux of DAF sludge. The higher the polymer dosage, at fixed solid concentration, the greater the rising velocity becomes. When applied with solid flux equations, a similar relationship to that of gravity thickening has been found. However, the values were much higher than in gravity thickening, because both the inflow solid concentration and the floating velocity were higher than for settled sludge. With this result, the proper dosage of polymer could be derived from the relationship between total solid flux and withdrawal velocity of DAF sludge.

The feasibility of electro-osmotic belt filter dewatering technology at pilot scale

Sewage sludge is typically dewatered using drying beds, belt filter presses or centrifuges. Mechanical dewatering of sludge is costly in terms of capital and running costs, especially the flocculent. In an attempt to address the need for more cost-effective dewatering technologies, electro-osmotic belt filtering was developed by Smollen and Kafaar in 1995. Themechanical equipment resembles a belt filter press but the belts are stainless steel, woven belts, which act as the electrodes. In this study, thefeasibility of the technology was tested at pilot scale using wasteactivated-, anaerobically digested- and dissolved air flotation sludge. The parameters which were investigated includes the applied voltage, polyelectrolyteusage and sludge feed rate. Applied voltage of between 15 and 25 volts increased the dewatering significantly in the waste activated- and anaerobically digested sludge. Applying a voltage in dissolved air flotation sludge could not enhance the efficiency of dewatering, unless stored to de-air. The technology was found as sensitive to polyelectrolyte dosages as belt presses. The performance of the electro-osmotic belt filter was sensitive to feed rate, but performed well with non-thickened waste activated sludge (0.61% solids), resulting in cake solids above 20%.

Co-digestion of waste organic solids: batch studies

Anaerobic digestion is a well established process for treating many types of organic waste, both solid and liquid. As such, the digestion of cattle slurries and of the organic fraction of municipal solid waste has been evaluated and has been successful. Attempts to apply the process to other types of solid organic waste, for example, to chicken manure, have met with limited success. In many areas of the UK, intensive chicken farming is leading to solids disposal problems. It has been proposed that co-digestion with cattle slurry could be a possible disposal route for chicken manure. In this study, cattle slurries were mixed with a range of solid wastes and allowed to digest in 1-1 batch digesters. The criteria for judging the success of a co-digestion were volatile solids (VS) reduction, total methane production and methane yield. In terms of the VS reductions (%), there was little difference between the various digestions. In terms of the cumulative methane production (1) the co-digestions with fruit and vegetable waste, the fish offal and the dissolved air flotation sludge were more effective than the digestion with cattle slurry alone. In terms of the specific methane yield (m 3 CH 4 kg −1 VS removed), the co-digestions containing fish offal and the brewery sludge gave higher values than the control digestion with cattle slurry alone. Compared with their control (cattle slurry alone), both co-digestions with poultry manure (7.5 and 15% TS) gave higher cumulative productions of methane and the system with the lower concentration of poultry manure gave a higher specific methane yield. However, there was some evidence of ammonia inhibition.

Land Disposal of Dissolved Air Flotation Sludge from Poultry Processing

ABSTRACT UNDIGESTED sludge from a dissolved air flotation unit (DAF) used to treat broiler processing plant wastewater was used as a nitrogen fertilizer source for corn production. A 1.7 ha field was divided into equal plots and duplicate test plots were applied with nitrogen from DAF skimmings at the rate of either 67 kg/ha or 135 kg/ha. Corn yields produced on these plots were compared to check plots which either ammonium nitrate or ammonium sulfate or no nitrogen had been applied. A test well for nitrate monitoring was placed in each plot. Results of this four year study have shown: Corn can be successfully grown using DAF sludge as the only nitrogen source. Increased nitrogen levels produced greater corn yields. When corn yields of DAF sludge-applied plots were compared to those using similar amounts of commercial nitrogen fertilizer, DAF sludge-applied plot yields were not found to be significantly different..

Research Note: Nutritive Value of Poultry By-Product Meal.: 3. Incorporation into Practical Diets

Studies were conducted to investigate the value of poultry by-product meal (PBPM) when incorporated into practical diets at low levels (5 to 10%). Samples from one plant, a Monday morning sample (fresh broiler waste) and a Friday afternoon sample (broiler and hatchery waste and dissolved air flotation sludge) were compared to a sample from another plant (fresh broiler waste). When the samples were incorporated at the 5% level into isocaloric, isonitrogenous corn-soy meal-based practical diets, no differences in 20-day gain or feed efficiency could be detected between the samples or in comparison with the effects of feeding an all-plant-based control diet in two experiments. Chick growth and feed efficiency were significantly depressed when PBPM was incorporated into the diet at the 10% level.