Acidification Strategy Research Articles

Effects of plasma treatment of digestates on pH, nitrification and nitrogen turnover during storage and after soil application

Acidification through plasma treatment technology presents a potential solution to mitigate nitrogen losses throughout the manure management chain, offering a dual benefit of atmospheric nitrogen incorporation into manures while inducing acidification. This study evaluated the use and effectiveness of plasma treatment technology as a one-time acidification strategy for digested slurry during long-term storage, its effects on slurry nitrogen (N) availability and subsequent release in the soil. A digestate from a full-scale anaerobic digester was separated using a decanter centrifuge, and the resultant liquid fraction (LF) was plasma treated to achieve three different initial pH levels (4.27, 5.03 and 5.42). After that, a storage experiment was set up for 180 days to monitor the evolution in pH and changes in NH4+, NO3- and NO2-. Concurrently, a soil incubation experiment was conducted to study the N turnover for 80 days after incorporating the organic materials (Liquid fraction, plasma-treated liquid fractions, digestate and raw slurry). Plasma treatment significantly increased total N and the proportion of inorganic N in the slurries by fixing atmospheric N as NO3- and NO2- and reduced the slurry pH depending on the treatment duration. After six months of storage, pH increased by 0.91 pH units in the plasma-treated liquid fraction with the highest initial pH (LFpH-5.42). Plasma treatment significantly increased net inorganic N release in soil by 5–14 % compared to a non-treated liquid fraction. Unexpected prolonged inhibition of NH4+ nitrification in soil for over 80 days after applying plasma-treated slurries was observed. In conclusion, plasma treatment emerges as a promising alternative to acid- and bio-acidification strategies, offering prolonged low slurry pH stabilisation, improved fertiliser value and delayed NH4+-N nitrification in soil.

Impact of potato trimming acidification on protein characteristics and bacterial community during long-term storage

Potato trimmings are a valuable by-product from potato processing containing both nutritional and functional potato protein. However, to allow delayed processing of trimmings, stabilisation methods should be implemented ensuring food safety and protein quality. In this study, acidification strategies by addition of different concentrations of organic acids i.e. acetic-, lactic- and citric acid were investigated as novel stabilisation methods for potato trimming and compared to natural acidification. Stabilisation was analysed and assessed by a variety of microbial, biochemical and protein characteristics.After 56 days of storage in acidified conditions, no decreases in true protein contents were observed despite changes in the protein molecular weight profile. In terms of food safety, yeast and mould inhibition during storage could solely be achieved by acetic acid addition, while lactic and citric acid could even result in increased unwanted growth. Therefore, acetic acid addition has been proven to be a successful stabilisation strategy.

Lysosomal dysfunction impairs mitochondrial quality control and is associated with neurodegeneration in TBCK encephaloneuronopathy.

Biallelic variants in the TBCK gene cause intellectual disability with remarkable clinical variability, ranging from static encephalopathy to progressive neurodegeneration (TBCK-Encephaloneuronopathy). The biological factors underlying variable disease penetrance remain unknown. Since previous studies had suggested aberrant autophagy, we tested whether mitophagy and mitochondrial function are altered in TBCK−/− fibroblasts derived from patients exhibiting variable clinical severity. Our data show significant accumulation of mitophagosomes, reduced mitochondrial respiratory capacity and mitochondrial DNA content, suggesting impaired mitochondrial quality control. Furthermore, the degree of mitochondrial dysfunction correlates with a neurodegenerative clinical course. Since mitophagy ultimately depends on lysosomal degradation, we also examined lysosomal function. Our data show that lysosomal proteolytic function is significantly reduced in TBCK−/− fibroblasts. Moreover, acidifying lysosomal nanoparticles rescue the mitochondrial respiratory defects in fibroblasts, suggesting impaired mitochondrial quality control secondary to lysosomal dysfunction. Our data provide insight into the disease mechanisms of TBCK Encephaloneuronopathy and the potential relevance of mitochondrial function as a biomarker beyond primary mitochondrial disorders. It also supports the benefit of lysosomal acidification strategies for disorders of impaired lysosomal degradation affecting mitochondrial quality control.

Autotrophic (C1-gas) versus heterotrophic (fructose) accumulation of acetic acid and ethanol in Clostridium aceticum

The influence of the carbon source on the metabolism and growth of Clostridium aceticum was investigated, supplying either CO or fructose as sole carbon source. The acid and solvent production patterns were determined under either autotrophic or heterotrophic conditions, elucidating the effect of pH on the substrate's bioconversion pattern. The highest maximum specific growth rate was observed with CO, under the organism's optimal growth conditions, reaching 0.052 h−1 and an acetic acid concentration of 18 g·L−1. The production of 4.4 g·L−1 ethanol was also possible, after medium acidification, during CO bioconversion. Conversely, formic acid inhibition was observed during fructose fermentation under optimal growth conditions. In the latter experiments, it was not possible to stimulate solvent production when growing C. aceticum on fructose, despite applying the same medium acidification strategy as with CO, showing the selective effect of the carbon source (autotrophic vs heterotrophic) on the metabolic pattern and solventogenesis.

182 The effects of pure benzoic acid, an acid blend product, or their combination in nursery pig diets on post-weaning growth performance

Abstract A total of 1,325 pigs (Camborough × line 800, PIC Canada) were weaned (20 d of age, 5.5 kg BW) and used to compare the effects of 5 diet acidification strategies on growth performance from d 0 to 41 post-weaning. Feed acidification strategies were fed over 3 dietary phases; d 0 to 13 (P1), d 13 to 20 (P2), and d 20 to 41 (P3). The 5 strategies consisted of 1) NC, commercial diet without any acidifier; 2) P+, NC with recommended 0.1% of an acidifier and flavoring blend (fumaric, sorbic, malic, citric acids with thymol, vanillin, eugenol) in P1, 0.05% in P2, and nothing added in P3; 3) VH, NC with 0.5% pure benzoic acid (VevoVitall®; DSM Nutritional Products) in P1, P2, and P3; 4) VL, NC with 0.25% pure benzoic acid in P1, P2, and P3; and 5) P+V, P+ with 0.5% pure benzoic acid in P1, 0.25% pure benzoic acid in P2, and nothing added in P3. Experimental additives were substituted for wheat in the basal diets. There were 10 pens of 26-27 pigs allotted to each acidification strategy in a RCBD based on initial BW. During P1, ADG, F/G, and d 13 BW were improved (P< 0.05) for pigs fed VH or P+V. In P2, ADG and d 20 BW were improved (P< 0.05) for pigs fed VH or P+V, and there was a tendency (P=0.06) for pigs fed acids (P+, VH, VL, or P+V) to have greater ADFI; however, there were no differences in F/G. There were no differences in growth performance during P3 or overall (d 0 to 41). Nevertheless, performance differences during P1 and P2 resulted in pigs fed an acidification strategy using pure benzoic acid (VH, VL, or P+V) having numerically greater BW (+0.5 kg) and income-over-feed-cost (+CA $0.44/pig) on d 41 when compared to pigs fed NC or P+.

A bottom-up acidification strategy engineered ultrathin g-C3N4 nanosheets towards boosting photocatalytic hydrogen evolution

At present, graphene-like carbon nitride (g-C3N4) has been considered as a promising photocatalyst for photocatalytic hydrogen gas (H2) evolution from water. The top-down treating of pristine bulk g-C3N4 (CN–B) by strong acid is an efficient modification way to improve photocatalytic performance, yet this strategy is environmental unfriendly because it requires higher strong acid concentration. To this end, here we firstly developed an available bottom-up acidification strategy to prepare the 2D ultrathin g-C3N4 nanosheets (UCNs) by the direct calcination of as-formed precursor derived from hydrothermal treating of melamine merely in diluted H2SO4 solution. As a result, the engineered UCNs with an average thickness of approximately 3 nm exhibited a remarkably enhanced visible-light-driven photocatalytic H2 evolved rate of 2590 μmol g−1 h−1 (λ > 400 nm), which is over 9.9-folds and 2.2-folds larger than that of CN–B and acid-treated g-C3N4 (CN-A) under the same condition, respectively. Our research offers a feasible and effective bottom-up acidification strategy for synthesizing the high-performance UCNs photocatalyst towards renewable solar energy conversion.

Enhanced hydrolysis and acidification strategy for efficient co-digestion of pretreated corn stover with chicken manure: Digestion performance and microbial community structure

The effect of enhanced hydrolysis and acidification (EHA) strategy on co-digestion performance of pretreated corn stover (CS) with chicken manure (CM) was investigated. The EHA process was applied to the CS pretreated with KOH and liquid fraction of digestate (LFD), prior to anaerobic digestion. The results showed that the efficiencies of hydrolysis and acidification for the pretreated CS group were significantly higher than the CS group. The maximum cumulative biomethane yield of 240.5 mL·gVS−1 and 242.0 mL·gVS−1 were obtained for the KOH CS group and LFD CS group during the EHA process at 1 day, showing 26.6% and 27.4% improvement over that of the control, respectively. T90 was shortened by 38.2%–44.1% and 17.7%–38.2%, correspondingly. The synergistic effects and hydrolysis kinetics were also enhanced by the EHA process. The communities of bacteria (Firmicutes, Proteobacteria, and Bacteroidetes) and archaea (Methanosaeta, Methanobacterium, and Methanosarcina) were enriched by the EHA process, and their interactions contributed to the improved digestion performance. Therefore, the EHA process was recommended for efficient biomethane conversion in co-digestion of CS and CM.

A one-step acidification strategy for sewage sludge dewatering with oxalic acid

Sewage sludge dewatering is an efficient approach to reduce the volume of sludge for the subsequent disposal. In this study, a novel one-step acidification sludge dewatering method was developed with using oxalic acid as a conditioner. In laboratory-scale experiments with the dosage of 200 mg/g dry solid (DS), the normalized capillary suction time and the specific resistance to filtration were respectively decreased by 78.7% and 60.0% after 30 min of oxalic acid conditioning, much more efficient than those conditioned with sulfuric acid and hydrochloric acid at the same pH value. This superior dewatering performance was attributed to two factors. One was that oxalic acid could more efficiently promote the hydrolysis of polysaccharide, especially pectins, to release bound water. The other was that OA could dissolve more Fe3+ and Al3+, as well as form precipitate with Ca2+ in sludge, which may act as flocculants or co-precipitator for the subsequent sludge particles coagulation. In pilot-scale experiments, the water content of oxalic acid conditioned sludge cake was reduced to 60% under the optimum conditions, while the reagent cost was as low as 110.0 USD/t DS. This work provides a cost-effective and easy-operated sewage sludge disposal technique, and also sheds light on the potential of oxalic acid in environmental waste treatment.

Oriented acidification of wasted activated sludge (WAS) focused on odd-carbon volatile fatty acid (VFA): Regulation strategy and microbial community dynamics

As the main intermediate metabolite in anaerobic digestion of wasted activated sludge (WAS), volatile fatty acids (VFAs) are proper substrate for mixed culture (MC) polyhydroxyalkanoate (PHA) synthesis. To further optimize the performance of MC PHA production process, VFA_odd (i.e., VFA with odd carbon atoms) oriented acidification process was proposed and conducted in this study. Three regulation factors including reaction pH, fraction of added β-cyclodextrin (β-CD) and glycerol were selected and response surface methodology (RSM) was used to enhance and effectively regulate the VFA_odd production while maintaining enough acidification degree in the WAS acidification. High percentage of VFA_odd (larger than 60% and dominated by propionic acid) can be obtained in the operating condition area with glycerol addition ratio (quantified by C/N) ranging from 15 to 20 and reaction pH ranging from 8.0 to 9.5 when β-CD addition was held at zero level (0.2 g/gTSS) according to the RSM. Semi-continuous acidification and MC PHA production assays further verified the reliability and effectiveness of the VFA_odd oriented acidification strategy. Microbial function group related to propionic acid production (Gprop) was defined based on the relationships between system function and microbial community structure, and 13 frequent species were found being involved in the Gprop. Roles of the group members in the oriented acidification were analyzed to understand the mechanisms of the regulation of VFA_odd production at microbial ecological level. A synergistic effect of WAS and glycerol on the VFA_odd production in the acidification process was revealed based on the ecological analysis.

Sequencing biological acidification of waste-activated sludge aiming to optimize phosphorus dissolution and recovery

ABSTRACTPhosphorus (P) recovery in wastewater treatment plants (WWTP) as pure crystals such as struvite (MgNH4PO4.6H2O), potassium struvite (KMgPO4.6H2O) and calcium phosphates (e.g. Ca3(PO4)2) is an already feasible technique that permits the production of green and marketable fertilizers and the reduction of operational costs. Commercial crystallizers can recovery more than 90% of soluble P. However, most of the P in WWTP sludge is unavailable for the processes (not dissolved). P solubilization and separation are thus the limiting steps in P-crystallization. With an innovative two-step sequencing acidification strategy, the current study has aimed to improve biological P solubilization on waste-activated sludge (WAS) from a full-scale plant. In the first step (P-release), low charges of organic waste were used as co-substrates of WAS pre-fermentation, seeking to produce volatile fatty acids to feed the P-release by Polyphosphate-accumulating organisms, while keeping its optimal metabolic pH (6–7). In this phase, milk serum, WWTP grease, urban organic waste and collective restaurant waste were individually applied as co-substrates. In the second step (P-dissolution), pH 4 was aimed at as it allows the dissolution of the most common precipitated species of P. Biological acidification was performed by white sugar addition, as a carbohydrate-rich organic waste model, which was compared to chemical acidification by HCl (12M) addition. With short retention times (48–96 h) and without inoculum application, all experiences succeeded on P solubilization (37–55% of soluble P), principally when carbohydrate-rich co-substrates were applied. Concentrations from 270 to 450 mg were achieved.

A life cycle perspective of slurry acidification strategies under different nitrogen regulations

Livestock manure is a major contributor to ammonia and greenhouse gas emissions and treatment technologies such as slurry acidification can be used to reduce both. In this study, life cycle assessment was used to compare impact potentials of slurry acidification at either the pig housing or the field application stage with conventional slurry management. Furthermore, the effects of differences in environmental regulations concerning nitrogen application limits were analysed. The impact categories analysed were terrestrial eutrophication potential, climate change potential, marine eutrophication potential and toxicity potential. Slurry acidification reduced the terrestrial eutrophication potential by 71% for in-house acidification and by 30% for field acidification. Changes in regulatory plant-available nitrogen application limits resulted in changes in climate change potential and marine eutrophication potential, with lower limits favouring in-house acidification. Acidification can substantially reduce the environmental impacts of animal slurry, but the effect depends on the context of the regulatory regime.

Local Acidification of Membrane Surfaces for Potentiometric Sensing of Anions in Environmental Samples.

The work dramatically improves the lower detection limit of anion selective membranes at environmental pH by using local acidification to suppress hydroxide interference at the membrane surface. Three separate localized acidification strategies are explored to achieve this, with ionophore-based membrane electrodes selective for nitrite and dihydrogen phosphate as guiding examples. In a first approach, a concentrated acetic acid solution (ca. 1 M) is placed in the inner filling solution of the PVC-based membrane electrode, forcing a significant acid gradient across the membrane. A second strategy achieves the same type of passive acidification by using an external proton source (fast diffusive doped polypropylene membrane) placed in front of a potentiometric solid contact anion selective electrode where the thin layer gap allows one to observe spontaneous acidification at the opposing detection electrode. The third approach shares the same configuration, but protons are here released by electrochemical control from the selective proton source into the thin layer sample. All three protocols improve the limit of detection by more than 2 orders of magnitude at environmental pH. Nitrite and dihydrogen phosphate determinations in artificial and natural samples are demonstrated.

An Investigation of pH Mediated Extraction and Precipitation of Phosphorus from Sludge Using Microfiltration: Processing and Costs

Membrane filtration of wastewater sludge is a feasible technology for the recovery of sustainable nutrients in bacteria and particle-free solutions. Diafiltration and acidification strategies were investigated for the recovery of phosphorus (P) from trout farm sludge. Extraction costs were determined using a pilot-scale unit. pH of 2.7 was found to maximize the extraction of P (and metals) and highest concentrations were achieved by acidic leaching of the sludge sediment. Levels of P, Ca, Fe, Mg, and K recovered in soluble fractions were 418 mg/L, 6730 mg/L, 66.8 mg/L, 29 mg/L, and 34.1 mg/L, respectively. Operational costs associated with acidification and power consumption were estimated to be 0.018 kWh/L permeate or 0.037 kWh/g P obtained. The extraction of P by membrane filtration was mainly dependent on pH and cost was considerably lower than that for P-based fertilizers. Owing to the high concentration of Ca and P in the permeate fractions, 99% of the soluble P was precipitated from solution at pH 8. Elemental analysis and FTIR of the precipitate obtained indicated to be carbonated calcium-deficient hydroxyapatite.

Fouling formation and chemical control in drip irrigation systems using treated wastewater

Drip irrigation systems are prone to changes in flow rate (FR) and increasing coefficients of variation (CV) when fed with treated wastewater, due to fouling inside the drippers. A model system was designed to measure the FR and fouling accumulation in laterals and drippers under different treatment conditions. A novel approach was taken to compare the different maintenance treatments. A comparison of chlorination and acidification strategies showed that daily chlorination and periodic acidification may prolong proper functioning of the drippers by maintaining a normal FR [(up to ±7 %) of nominal FR] and CV (<7 %) index in correlation with low fouling accumulation in the pipeline (<0.01 mg deposit/cm pipe 2 ). Current recommendations for the frequency of conventional treatments were found to be insufficient. Chemical analyses of the fouling inside the dripper and accumulated on the pipe wall showed that biofilm can survive inside the dripper under harsh environmental conditions, even when the pipeline stays clean. These results shed light on biofilm growth and survival mechanisms inside the dripper and may pave the way to developing new treatments or improving dripper design.

Fabrication of large volume, macroscopically defined and responsive engineered emulsions using a homogeneous pH-trigger

Hydrolysis of glucono-δ-lactone (GδL) lowers the pH homogeneously throughout an aqueous solution. We exploit this non-invasive pH-trigger to prepare significant volumes of kinetically trapped, functional and responsive emulsion droplet assemblies—engineered emulsions—from highly stable polymer-functionalized emulsion droplets. In contrast to conventional acidification strategies, such as the addition of concentrated acid solutions, this approach also allows the kinetics of engineered emulsion formation to be monitored by rheometry thus providing valuable insight into the formation process. Engineered emulsions with enhanced morphological and compositional complexity can be prepared using GδL while maintaining reversibility—that is, the assembled droplets can be rapidly disassembled into free-flowing emulsion dispersions without compromising the droplet integrity. These developments may facilitate the broad exploitation of this generic new encapsulation and reversible assembly technology.

Uncertainties in Large Scale Assessments of Critical Load Exceedances

In the 1999 Gothenburg protocol to the UN/ECE LRTAP Convention andin the negotiations for an EU acidification strategy the area withexceedances of critical loads has been the preferred measure forenvironmental impacts. The aim of this study has been to assessthe influence of the uncertainty and spatial variation of both thecritical loads and deposition values on the calculated area withexceedances of critical loads. This has been done on a nationalscale for Denmark and on the European scale based on the dataincluded in the RAINS model. It is demonstrated that includinguncertainty and spatial variation in exceedance calculations, ingeneral gives larger exceeded area for the critical load ofacidity, CL(A). The picture for the critical load of nutrientnitrogen, CLnut(N), is more mixed because of the higherproportion of exceeded areas. A further point of interest is thepossibility of validating relationships between critical loadexceedances and observable damage based on large scale monitoringand model data. It is demonstrated that it will probably not bepossible to use exceedance calculations on European scale as basisfor validation exercises, linking exceedances to observable damage.

The EU Acidification Strategy: Sensitivity of calculated emission ceilings for nitrogen and sulphur for Denmark

The sensitivity of the calculated emission ceilings to changes and uncertainties in preconditions used in the cost-effective optimisations for the EU Acidification Strategy is evaluated and the uncertainties on the optimisations are discussed. The total uncertainties on the deposition targets are estimated to be in the range of 20–30% and depend on uncertainties in the deposition calculations, in the critical loads calculations, and the shape and number of receptor points in the cumulated frequency distribution curve used for the optimisation. Using this uncertainty range it is found that the deposition target in a limited number of grids has a significant influence on the cost of the optimal solution for Denmark. The emission ceilings for Denmark are sensitive to changes in the input energy scenario, but the sensitivity to changes and uncertainty in marginal costs is limited. The use of new emission factors for ammonia in Denmark has the potential to change the emission ceilings for SO 2 and NO x allowing higher emissions for the energy sector.

The limitations of integrated assessment modelling in developing air pollution control policies

Integrated assessment models such as the IIASA RAINS model have been used in developing pollution control policies in Europe over recent years. Large uncertainties occur in all subunits of such models, especially in energy scenarios, abatement costs, emission-deposition-transport relationships, and the definition of the environmental targets. The effects of these uncertainties, together with errors in input data, have been investigated for the RAINS 7.2 modelling used in developing the initial EU Acidification Strategy proposals. Changes in input data, well within these uncertainties, can lead to significantly different “optimal” strategies, with large differences in absolute levels of costs and their distribution between countries. It may be concluded that the outputs of integrated assessment models can only be a guide to policymaking, and should not be accepted uncritically. Model output should always be accompanied by a full uncertainty analysis, and the model and data used should be subject to thorough peer review.

NO x emission abatement in EU power stations: results and response to the acidification strategy

Following discussions on acidification in the eighties, the European Community came to a decision on NO x emission by power stations in the framework of Directive 88/609/EC on the limitation of emissions of certain pollutants from Large Combustion Installations. Within the Member States different strategies and technical measures have been applied to meet the obligations. It appears that the target for the year 1998 was already met in 1990 for the average emissions of LCI in the Community as a whole. As an example of recent developments the power station emissions in the Netherlands will be presented. The European Community is developing a Community strategy to combat acidification. The Electricity Supply Industry has serious reservations about the strategy. This will be discussed together with a case study for the Netherlands. It will be shown that RAINS is not an appropriate tool for quantitative allocation of emission reduction goals to the Member States of the European Community. A strategy is preferred that proceeds by successive stages, accompanied by monitoring of the environmental improvements. This approach enables us to integrate the progress achieved in environmental quality and emission reduction techniques into modelling works and cost/benefits assessment studies.