Thermophilic and mesophilic temperature phase anaerobic codigestion (TPAcD) compared with single-stage co-digestion of sewage sludge and sugar beet pulp lixiviation

The performance of temperature phase anaerobic co-digestion (TPAcD) for sewage sludge and sugar beet pulp lixiviation (using the process of exchanging the digesting substrate between spatially separated thermophilic and mesophilic digesters) was tested and compared to both single-stage mesophilic and thermophilic anaerobic co-digestion. Two Hydraulic Retention Times (HRT) were studied in the thermophilic stage of anaerobic digestion in two temperature phases, maintaining the optimum time of the mesophilic stage at 10 days, obtained as such in single-stage anaerobic co-digestion. In this way, we obtained the advantages of both temperature regimes. Volatile solids removal efficiency from the TPAcD system depended on the sludge exchange rate, but fell within the 72.6e64.6% range. This was higher than the value of 46.8% obtained with single-stage thermophilic digestion and that of 40.5% obtained with mesophilic digestion. The specific methane yield was 424e468 ml CH4 per gram of volatile solids removed, similar to that of single-stage mesophilic anaerobic digestion. The increase in microbial activity inside the reactor was directly proportional to the organic loading rate (OLR) (or inversely proportional to the HRT) and inversely proportional to the size of the microbial population in single-stage anaerobic co-digestion systems

Seeking to enhance the bioenergy of municipal sludge: Effect of alkali pre-treatment and soluble organic matter supplementation

The aim of this research is to enhance the mesophilic anaerobic digestion of municipal sludge from Cadiz-San Fernando (Spain) wastewater treatment plant at 20 days hydraulic retention time (HRT). Two different strategies were tested to improve the process: co-digestion with the addition of soluble organic matter (1% v/v); and alkali sludge pre-treatment (NaOH) prior to co-digestion with glycerine (1% v/v). Methane production (MP) was substantially enhanced (from 0.36 ± 0.09 L CH4 l/d to 0.85 ± 0.16 L CH4 l/d), as was specific methane production (SMP) (from 0.20 ± 0.05 L CH4/g VS to 0.49 ± 0.09 L CH4/g VS) when glycerine was added. The addition of glycerine does not seem to affect sludge stability, the quality of the effluent in terms of pH and organic matter content, i.e. volatile fatty acids (VFA), soluble organic matter and total volatile solid, or process stability (VFA/Alkalinity ratio < 0.4). Alkali pre-treatment prior to co-digestion resulted in a high increase in soluble organic loading rates (more than 20%) and acidification yield (more than 50%). At 20 days HRT, however, it led to overload of the system and total destabilization of the mesophilic anaerobic co-digestion of sewage sludge and glycerine

Mesophilic anaerobic co-digestion of sewage sludge with glycerine: Effect of solids retention time

The main objective of this paper is to examine the effect of the increase in organic loading rates (OLRs), by reducing the solids retention time (SRT) from 20 d to 5 d, in single-phase mesophilic anaerobic co-digestion of sewage sludge with glycerine (1% v/v). It was experimentally confirmed that anaerobic co-digestion of these biowastes under steady-state conditions can achieve an 85 ± 5% reduction in volatile fatty acids (VFA) at SRTs of between 20 and 9 d, with a methane production yield of around 0.8 l CH4/l/d. Decreases in the SRT not only allow the sludge stability and biogas production to be maintained, but also lead to an increase in the waste that could be treated and lower operating costs. Therefore, mesophilic anaerobic co-digestion of sewage sludge and glycerin at a SRT lower than 20 d is possible and preferable due to being more economical and environmentally friendl

Improvement of biomethane potential of sewage sludge anaerobic co-digestion by addition of “sherry-wine” distillery wastewater

Co-digestion of sewage sludge (SS) with other unusually treated residues has been reported as an efficient method to improve biomethane production. In this work, Sherry-wine distillery wastewater (SWDW) has been proposed as co-substrate in order to increase biomethane production and as a breakthrough solution in the management of both types of waste. In order to achieve this goal, different SS:SW-DW mixtures were employed as substrates in Biomethane Potential (BMP) tests. The biodegradability and biomethane potential of each mixture was determined selecting the optimal co-substrate ratio. Results showed that the addition of SW-DW as a co-substrate improves the anaerobic digestion of SS in a proportionally way in terms of CODs and biomethane production The optimal co-substrates ratio was 50:50 of SS:SW-DW obtaining %VSremoval ¼ 54.5%; YCH4 ¼ 225.1 L CH4/kgsv or 154 L CH4/kgCODt and microbial population of 5.5 times higher than sole SS. In this case, %VSremoval ¼ 48.1%; YCH4 ¼ 183 L CH4/ kgsv or 135 L CH4/kgCODt. The modified Gompertz equation was used for the kinetic modelling of biogas production with successful fitting results (r2 ¼ 0.99). In this sense, at optimal conditions, the maximum productivity reached at an infinite digestion time was (YMAX CH4 ) ¼ 229 ± 5.0 NL/kgSV; the specific constant was K ¼ 25.0 ± 2.3 NL/kgSV$d and the lag phase time constant was (l) ¼ 2.49 ± 0.1

Improvement of the anaerobic digestion of sewage sludge by co-digestion with wine vinasse and poultry manure: Effect of different hydraulic retention times

This study arose in response to the management of different organic wastes generated locally, which cause environmental damage. These wastes could be used to obtain biogas and class A biosolids through anaerobic digestion. For this purpose, the mesophilic anaerobic tri-digestion of sewage sludge (S), wine vinasse (V) and poultry manure (PM) (49.5:49.5:1) was studied to obtain biogas in an improved way compared to bi-digestion of SV (50:50) and mono-digestion of S. Tests were carried out in anaerobic digesters, at laboratory scale, to compare the benefits at different hydraulic retention time (HRT) (20, 15, 13, 10, 8 and 6 days). From the results obtained, anaerobic tri-digestion of the waste gave the best results, with a total chemical oxygen demand (TCOD) removal efficiency of 51%, volatile solids (VS) removal efficiency of 57%, and methane yield values of 261 mLCH4/gVSadded at a HRT of 13 days. In relation to the pathogens, both co-digestion studies addressed managed to inactivate enough pathogens in the effluent to be classified as class A biosolids. This would allow considering the anaerobic tri-digestion as a promising technology, which allows valorizing organic waste, obtaining biogas and class A biosolids, moving towards a circular bioeconomy. © 2022 The Author(s)This study has been funded by the Project Management of agro-food waste and sludge within the framework of the circular economy: energy and fertilizer production through anaerobic codigestion in a pilot plant (P18-RT-1348) of the Andalusian Research, Development and Innovation Plan (PAIDI 2020)

Temperature-phased enhanced the single-stage anaerobic co-digestion of sewage sludge, wine vinasse and poultry manure: Perspetives for the circular economy

The effect of hydraulic retention time (HRT) on single-stage (mesophilic and thermophilic range) and temperature-phase anaerobic co-digestion processes (TPAD) of sewage sludge, wine vinasse, poultry manure was studied. The HRTs studied were 20, 15, 13 and 10 days for the single-stage and TPAD process. For the TPAD with an HRT of 20 days, 65 % of total chemical oxygen demand (TCOD) were removed, which was higher than the single-stage process (26 % and 17 % TCOD removal, respectively for the thermophilic and mesophilic phases). Regarding the volatile solids (VS) removal, TPAD process presented a higher efficiency (90 %) when compared with the thermophilic (41 %) and mesophilic (43 %) single-stage digesters. At an HRT of 13 days 155 mLCH4/ gVSadded (thermophilic), 260 mLCH4/gVSadded (mesophilic), and 202 mLCH4/gVSadded (TPAD) were obtained. The maximum methane yield was achieved for the TPAD process operated at an HRT of 20 days (320 mLCH4/ gVSadded) with the additional benefit of obtaining hydrogen in the first stage (40.41 mLH2/gVSadded). The digestate obtained from the TPAD process were classified as class A biosolids, and could be used for agriculture fertilizer. In conclusion, TPAD waste management process presented better operational performance and methane yield when compared to a single-stage conventional system, direcly contributing for the framework of a circular economy transition of the agri-food industry

Thermophilic-mesophilic temperature phase anaerobic co-digestion of sewage sludge, wine vinasse and poultry manure: Effect of hydraulic retention time on mesophilic-methanogenic stage

The present study investigated the influence of the hydraulic retention time (HRT) in temperature-phase anaerobic co-digestion (TPAcD) for methane production. The reactors were started-up with a mixing ratio of 49.5:49.5:1 of sewage sludge, wine vinasse and poultry manure. The TPAcD was operated at thermophilic temperatures in the first stage and mesophilic temperatures in the second stage. The thermophilic stage operated with a constant HRT of 5 days, while the methanogenic stage was optimized under the HRT of 15, 12, 10, 8, 5, 4, and 3 days. The best results were obtained for an HRT of 12 days in the methanogenic stage, 56.35 % of volatile solids (VS) biodegradation was achieved, with a methane yield of 391 mL CH4/gVSadded. Regarding the whole TPAcD process (acidogenic following by methanogenic), the vS and total volatile fatty acids reached, respec-tively, 93.13 % and 97.43 % of removal efficiency. The microbial population revealed that Eubacteria was higher than the Archaea at the HRT with the highest methane yield, and the microbial activity increased proportionally to the organic loading rate, which in turn was related to methane production. Due to the strong pathogen reduction in the TPAcD, the digestate obtained can be classified as class A biosolids in all HRT evaluated, being a promising alternative for its application as agricultural fertilizer. Finally, the presented TPAcD process can be an environmeltally friendly alternative for the management of sewage sludge, wine vinasse, and poultry manure in an integrated biorefinery for the recovery of bioenergy and fertilizer, advocating a sustainable approach for the circular economy transition

Effect of temperature on biohydrogen and biomethane production using a biochemical potential test with different mixtures of sewage sludge, vinasse and poultry manure

A two-stage anaerobic co-digestion system has been proposed, comprising a first acidogenic stage at different temperatures, where biohydrogen is obtained; and a second mesophilic methanogenic stage where biomethane is obtained. The objective of this research was to evaluate the biochemical hydrogen potentials (BHP) at different temperature ranges, and their effect on the biochemical methane potentials subsequently carried out with the effluents from the BHP, in batch trials. Also, to evaluate the effect of adding a third co-substrate (poultry manure) to the mixture of sewage sludge and wine vinasse. For the BHP tests, temperatures of 35°, 55° and 70 °C were tested in mixtures of sewage sludge:vinasse (50:50) and sewage sludge:vinasse:poultry manure (49.5:49.5:1). It was found that the addition of poultry manure and a thermophilic temperature of 55 °C was ideal for biohydrogen generation with the highest recorded yield of 27.1mLH2/gVS. In the BMP trials consisting of effluent from the BHP and programmed at 35 °C, it was found that the effluent from the hyperthermophilic BHP trials (70 °C) generated more biogas and had a higher methane yield (117.36 mLCH4/gVS), and that this yield was higher for the sewage sludge and vinasse mixture alone. This proportion also had the highest percentage of VS removal (45.74%). The Modified Gompertz model was the best fit to the experimental data, with R2 > 0.983 in all cases. The search for the most suitable temperature ranges for the production of H2 and CH4 is necessary in order to be able to efficiently realise this technology on a larger scale. © 2022 The Author

Kinetic modelling of anaerobic co-digestion of sewage sludge and Sherry-wine distillery wastewater: Effect of substrate composition in batch bioreactor

Batch thermophilic anaerobic co-digestion of sewage sludge (SS) and Sherry-wine distillery wastewater (SW-DW) was investigated through biochemical methane potential tests (BMP). The results pointed out that biodegrad-ability and biomethane potential were enhanced proportionally to the percentage of SW-DW of the feedstock, whose soluble biodegradability fraction is 10-fold higher than SS. Specifically, organic matter removal increases from 37 % (employing sole SS as feedstock) to 60 % (employing sole SW-DW as feedstock). SW-DW almost doubles methane yield in comparison to SS (302 +/- 15 and 175 +/- 9 NL/kg, respectively). A structured kinetic model was developed considering hydrolysis, acidogenic and methanogenic steps of anaerobic digestion. A non-linear multiple-response regression was employed to estimate the kinetic parameters for each feedstock (0%(v/v) SW-DW, 25%(v/v) SW-DW, 50%(v/v) SW-DW, 75%(v/v) SW-DW, and 100%(v/v) SW-DW). The first-order kinetic parameter estimated of the hydrolysis step varies inversely proportional to the percentage of SW-DW content in the feedstock. Whereas, there is no significant influence of feedstock compo-sition on kinetic parameters value regarding acidogenesis and methanogenesis. These results showed that rate-limiting step switched during the fermentation and the addition of SW-DW favours acidogenic and meth-anogenic steps. In summary, the proposed kinetic model was able to predict batch experimental data, supporting the application of biogas production from anaerobic co-digestion of SS and DW-DW

Biomethane production improvement by enzymatic pretreatments and enhancers of sewage sludge anaerobic digestion

Enzymatic hydrolysis is recognised as an effective pre-treatment for increasing biodegradability of sludge. In this work, isolated commercial enzymes as well as in-situ enzymes producer bacteria were used respectively as enhancers and pre-treatments of sewage sludge. Biodegradability of sample as well as biomethane potential production were studied. Results showed that depuration efficiencies in terms of CODs (73.5-85.5 %) and TVS (28.5-42.7 %) were more than twice the control value. In addition, pre-treated samples as well as enhanced samples with enzymes generated more biomethane than control. The optimal ones, were those with the isolated proteases (P) and with bacteria (Bacillus licheniformis) treatment in-situ (F), producing a total volume of 72.4 ± 2.62 ml CH4 and 114 ml ± 0.46 CH4, respectively, increasing the biogas volume in 3.65 and 5.77 times respectively compared with control