Occurrence of pharmaceuticals in the wastewater of a Greek hospital: Combining consumption data collection and LC-QTOF-MS analysis.

In this article we applied drug consumption approach and chemical analysis in parallel to investigate the concentrations of a large number of pharmaceuticals in different streams of a General Hospital. Drugs consumption data was collected during two periods (Period 1, 2) and the predicted environmental concentrations (PECs) were estimated for the wastewater of a building housing specific medical services (Point A) and for the entire hospital (Point B). Hospital wastewater samples (HWW) samples were also collected from these points and periods and the measured environmental concentrations (MEC) were determined using UHPLC-ESI-QTOF-MS/MS. According to consumption data, the highest number of drugs was consumed in the departments of Hematology, Intensive Care Unit, Cardiology, Internal Medicine, and Oncology, while the number of active substances used in the hospital was 413 (Period 1) and 362 (Period 2). For most substances, much higher PEC and MEC values were found at the HWW of Point A indicating that on-site treatment of this stream could be examined in the future. The application of wide-scope target analysis allowed the quantification of 122 compounds, while 21 additional substances were identified using suspect screening. The highest mean concentrations in Period 1 were found for acetaminophen (1100 µg/L) and rifaximin (723 µg/L), while in Period 2 for iopromide (458 µg/L) and acyclovir (408 µg/L). Among the detected compounds, 19 metabolites were determined. Atenolol acid, 1-hydroxy-midazolam and clopidogrel carboxylic acid were quantified at concentrations much higher than parent compounds indicating the importance of metabolites' monitoring in HWW. Calculation of PEC/MEC ratio for 36 pharmaceuticals showed sufficient correlation of these values for 19 % to 33 % of the substances depending on the examined period and sampling point. The parallel collection of drugs consumption data and chemical analysis give a thorough picture of the substances present in HWW and their main sources, facilitating decision-making for their better management.

Removal of microfiber in vertical flow constructed wetlands treating greywater.

Nature-based solutions such as constructed wetlands (CW) are considered as a sustainable, green technology for greywater treatment. However, their efficiency to remove microplastics is not well-known even though greywater is considered as a significant source of microfiber pollution. In this study, the removal of fiber microplastics from greywater using a vertical flow constructed wetland (VFCW) was investigated. For the purposes of this study, an experimental wetland was constructed, planted with the flowering plant Zantedeschia aethiopica and filled with a substrate made of sand/gravel of several sizes. The system's performance was monitored for five months during which it received real laundry wastewater. Promising results were obtained showing the significant removal of microfibers from the influent (> 95 %). Moreover, the ability of the system to remove microfibers from laundry wastewater was not significantly affected from the hydraulic loading rate (HLR) applied. The average microfibers concentration decreased from 71 ± 25 microparticles/L in the influent to 1 ± 1 microparticles/L in the effluent of VFCW when an HLR of 63.7 mm/d was applied. High removal efficiencies were also observed for COD and turbidity (93 % and 94 %, respectively). Thus, the results indicate a significant improvement in the overall quality of laundry wastewater due to the use of the VFCW.

Use of green roofs for greywater treatment: Role of substrate, depth, plants, and recirculation.

This work focuses on the use of green roof as a modified shallow vertical flow constructed wetland for greywater treatment in buildings. Different design parameters such as substrate (perlite or vermiculite), substrate depth (15 cm or 25 cm), and plant species (Geranium zonale, Polygala myrtifolia or Atriplex halimus) were tested to determine optimum selection. In addition, the application of a 40% recirculation rate was applied during last month of the experiment to quantify the efficiency of pollutants removal. The experiment was conducted for a period of 12 months under typical Mediterranean climatic conditions in Lesvos island, Greece. Results showed that green roofs planted with Atriplex halimus and filled with 20 cm of vermiculite had the best COD (91%), BOD (91%), TSS (93%) and turbidity (93%) average removal efficiencies. In contrast, significant lower removals were observed when the substrate depth was decreased to 10 cm (60-75%). Green roof vegetation had significant impact on TN removal as the average TN concentration decreased from 6.5 ± 1.8 mg/L in the effluent of unplanted systems to 4.9 ± 2.7 mg/L in the effluent of green roofs planted with Atriplex halimus. The recirculation of a portion of the effluent in the influent had as a result a significant improvement of turbidity, organic matter and (especially) nitrogen removal. For example, BOD removal in green roofs planted with Atriplex halimus and filled with 20 cm of perlite increased from 76% to 92%, while TN removal in green roofs planted with the same plants and filled with 20 cm of vermiculite increased from 56% to 87%. Overall, the operation of green roofs as modified vertical unsaturated constructed wetlands seems a sustainable nature-based solution for greywater treatment and reuse in urban areas.

Converting treatment wetlands into "treatment gardens": Use of ornamental plants for greywater treatment.

Nowadays, the use of constructed wetlands for on-site greywater treatment is a very promising option. The successful application of this nature-based solution at full scale requires public acceptance, economic feasibility and the production of high-quality treated greywater. This work focuses on the use of ornamental plants as vertical flow constructed wetland (VFCW) vegetation for greywater treatment, aiming to improve aesthetic and acceptability of the system. The performance and economic feasibility of the proposed green technology were examined during a 2-years study. Results show that Pittosporum tobira and Hedera helix can grow in VFCW operating with greywater without any visible symptoms. These species tolerated both drought and flooding conditions, making them ideal for use not only in residential buildings but also in seasonal hotels and holiday homes. In contrast, partial defoliation of Polygala myrtifolia plants was observed during the winter period. High average removal efficiencies were observed for BOD (99%), COD (96%) and TSS (94%) in all examined VFCWs including unplanted beds. Phosphorus removal gradually decreased from 100% during first months of operation to 15% during second year of operation. In addition, total coliforms concentration reduced by 2.2 log units in the effluent of all planted systems, while lower removal efficiency was observed in the absence of plants. The mean concentration of BOD and TSS in the treated greywater met the standards for indoor reuse (<10 mg/L). Cost payback periods for the installation of the proposed technology in a multi-family building, a single house and a hotel in Greece were found 4.7, 16.6 and 2.5 years, respectively. Overall, the "treatment gardens" proposed in this study provide a technically and economically feasible solution for greywater treatment, with the additional benefit of improving the aesthetic of urban, semi-urban and touristic areas.

Effects of treated wastewater irrigation on the establishment of young grapevines.

Irrigation with treated wastewater could produce excessive accumulations within the plant and soil, negatively affecting the yield and production quality. In addition, the presence of biological and chemical contaminants could harm the agricultural environment, as well as the health of farmers and consumers. During this work, the suitability of secondary and tertiary treated wastewater for use in young grapevines was evaluated by studying the effect of the wastewater irrigation on the soil-plant system, crop yield, fruit quality and the presence of inorganic chemical contamination (salts, elements and heavy metals), organic chemical contamination (polycyclic aromatic hydrocarbons) and microbial contamination (E. coli, total coliforms). The results show that tertiary treated wastewater had positive impact on plant growth and yield while secondary treated wastewater had negative impact on fruit safety in comparison with tap water. Sodium levels in soils irrigated with treated wastewater increased at the end of the irrigation period while decreased during the wet season. The total polycyclic aromatic hydrocarbon concentrations in the soils ranged from 363 µg/kg to 374 µg/kg at the end of the experiment for all irrigation treatments applied. The use of tertiary treated wastewater was recommended for the irrigation of young grapevines as an alternative water source secured protection of environment, plant health and fruit quality.

Production of organic fertilizer from olive mill wastewater by combining solar greenhouse drying and composting.

Olive mill wastewater (OMW) is generated during the production of olive oil. Its disposal is still a major environmental problem in Mediterranean countries, despite the fact that a large number of technologies have been proposed up to date. The present work examines for the first time a novel, simple and low-cost technology for OMW treatment combining solar drying and composting. In the first step, OMW was dried in a chamber inside a solar greenhouse using swine manure as a bulking agent. The mean evaporation rate was found to be 5.2 kg H2O/m2/d for a drying period of 6 months (February-August). High phenol (75%) and low nitrogen (15%) and carbon (15%) losses were recorded at the end of the solar drying process. The final product after solar drying was rich in nutrients (N: 27.8 g/kg, P: 7.3 g/kg, K: 81.6 g/kg) but still contained significant quantities of phenols (18.4 g/kg). In order to detoxify the final product, a composting process was applied as a second step with or without the use of grape marc as bulking agent. Results showed that the use of grape marc as a bulking agent at a volume ratio of 1:1 achieved a higher compost temperature profile (60 °C) than 2:1 (solar drying product: grape marc) or no use (solar drying product). The end product after the combination of solar drying and composting had the characteristics of an organic fertilizer (57% organic carbon) rich in nutrients (3.5% N, 1% P, 6.5% K) with quite low phenol content (2.9 g/kg). Finally, the use of this product for the cultivation of pepper plants approved its fertility which was found similar with commercial NPK fertilizers.

Halophytes as vertical-flow constructed wetland vegetation for domestic wastewater treatment.

Recent findings show that halophytes have the ability to accumulate salts in their tissues, making them a very interesting group of plants for domestic wastewater treatment in constructed wetlands (CWs). In that case, it might be possible to reduce the salinity of the final effluent, which is a crucial parameter for wastewater reuse in agriculture. During this study three halophytes, Atriplex halimus, Juncus acutus and Sarcocornia perennis, were tested for phyto-desalination of domestic wastewater in a vertical flow constructed wetland (VFCW) and compared with common reeds (Phragmites australis). In addition, the effect of this alternative vegetation on the overall performance of the system regarding organic matter, nutrients, boron and pathogen removal was monitored. The organic loading rate (OLR) was about 21gCOD/m2/d and the hydraulic loading rate (HLR) was 95mm/d in both cases. Promising results were obtained for A. halimus, which shows high biomass productivity and significant capability to accumulate salts, mainly Na, in its tissues. A positive effect on pathogen removal efficiency was also recorded. However, nitrogen concentration in the effluent of the VFCW planted with halophytes was found to be higher than in the effluent of the VFCW planted with reeds. Finally, no significant effect on organic matter and phosphorus removal efficiency was observed from the use of halophytes in place of reeds.

Single house on-site grey water treatment using a submerged membrane bioreactor for toilet flushing.

Wastewater recycling has been and continues to be practiced all over the world for a variety of reasons including: increasing water availability, combating water shortages and drought, and supporting environmental and public health protection. Nowadays, one of the most interesting issues for wastewater recycling is the on-site treatment and reuse of grey water. During this study the efficiency of a compact Submerged Membrane Bioreactor (SMBR) system to treat real grey water in a single house in Crete, Greece, was examined. In the study, grey water was collected from a bathtub, shower and washing machine containing significant amounts of organic matter and pathogens. Chemical oxygen demand (COD) removal in the system was approximately 87%. Total suspended solids (TSS) were reduced from 95mgL(-1) in the influent to 8mgL(-1) in the effluent. The efficiency of the system to reduce anionic surfactants was about 80%. Fecal and total coliforms decreased significantly using the SMBR system due to rejection, by the membrane, used in the study. Overall, the SMBR treatment produces average effluent values that would satisfy international guidelines for indoor reuse applications such as toilet flushing.

Co-digestion of sewage sludge with glycerol to boost biogas production.

The feasibility of adding crude glycerol from the biodiesel industry to the anaerobic digesters treating sewage sludge in wastewater treatment plants was studied in both batch and continuous experiments at 35 degrees C. Glycerol addition can boost biogas yields, if it does not exceed a limiting 1% (v/v) concentration in the feed. Any further increase of glycerol causes a high imbalance in the anaerobic digestion process. The reactor treating the sewage sludge produced 1106+/-36 ml CH(4)/d before the addition of glycerol and 2353+/-94 ml CH(4)/d after the addition of glycerol (1% v/v in the feed). The extra glycerol-COD added to the feed did not have a negative effect on reactor performance, but seemed to increase the active biomass (volatile solids) concentration in the system. Batch kinetic experiments showed that the maximum specific utilization rate (mu(max)) and the saturation constant (K(S)) of glycerol were 0.149+/-0.015 h(-1) and 0.276+/-0.095 g/l, respectively. Comparing the estimated values with the kinetics constants for propionate reported in the literature, it can be concluded that glycerol uptake is not the rate-limiting step during the process.

Fate and effect of linuron and metribuzin on the co-composting of green waste and sewage sludge.

The fate and effect of the herbicides linuron and metribuzin on the co-composting of sewage sludge and green waste were addressed in this work. The experiments were conducted in metal cubic containers of 1.0m(3) volume simulating a windrow composting system. A mixture of sludge and green waste was prepared at a ratio of 1:5 v/v. The mixture was split in four equal parts and the two herbicides were added, using a pressure sprayer, as sole or mixed pollutant in each of the three mixtures. The forth mixture was composted without any addition of herbicide, to serve as control. Temperature, physicochemical characteristics, herbicide concentration, carbon dioxide emission, methane emission and microbiological parameters were measured either daily or every time the mixtures were turned, for a period of 80 days. Both herbicides' concentration decreased significantly resulting in removal efficiencies of 99.1-99.7% and 95.8-96.0% for linuron and metribuzin, respectively. Incubation of microbiologically inactive mixtures at a temperature schedule following the spontaneous temperature evolution in the composters resulted in very little (1-11%) decomposition for both herbicides. Comparison of the variation of physicochemical parameters and microbial populations during composting indicated that both herbicides did not affect the composting process.

Enhanced methane and hydrogen production from municipal solid waste and agro-industrial by-products co-digested with crude glycerol.

The effects of crude glycerol on the performance of single-stage anaerobic reactors treating different types of organic waste were examined. A reactor treating the organic fraction of municipal solid waste produced 1400 mL CH(4)/d before the addition of glycerol and 2094 mL CH(4)/d after the addition of glycerol. An enhanced methane production rate was also observed when a 1:4 mixture of olive mill wastewater and slaughterhouse wastewater was supplemented with crude glycerol. Specifically, by adding 1% v/v crude glycerol to the feed, the methane production rate increased from 479 mL/d to 1210 mL/d. The extra glycerol-COD added to the feed did not have a negative effect on the reactor performance in either case. Supplementation of the feed with crude glycerol also had a significant positive effect on anaerobic fermentation reactors. Hydrogen yield was 26 mmole H(2)/g VS added and 15 mmole H(2)/g VS added in a reactor treating the organic fraction of municipal solid waste and a 1:4 mixture of olive mill and slaughterhouse wastewater. The addition of crude glycerol to the feed enhanced hydrogen yield at 2.9 mmole H(2)/g glycerol added and 0.7 mmole H(2)/g glycerol added.

Pilot-scale comparison of constructed wetlands operated under high hydraulic loading rates and attached biofilm reactors for domestic wastewater treatment.

Four different pilot-scale treatment units were constructed to compare the feasibility of treating domestic wastewater in the City of Heraklio, Crete, Greece: (a) a free water surface (FWS) wetland system, (b) a horizontal subsurface flow (HSF) wetland system, (c) a rotating biological contactor (RBC), and (d) a packed bed filter (PBF). All units operated in parallel at various hydraulic loading rates (HLR) ranging from 50% to 175% of designed operating HLR. The study was conducted during an 8 month period and showed that COD removal efficiency of HSF was comparable (>75%) to that of RBC and PBF, whereas that of the FWS system was only 57%. Average nutrient removal efficiencies for FWS, HSF, RBC and PBF were 6%, 21%, 40% and 43%, respectively for total nitrogen and 21%, 39%, 41% and 42%, respectively for total phosphorus. Removals of total coliforms were lowest in FWS and PBF (1.3 log units) and higher in HSF and RBC (2.3 to 2.6 log units). HSF showed slightly lower but comparable effluent quality to that of RBC and PBF systems, but the construction cost and energy requirements for this system are significantly lower. Overall the final decision for the best non-conventional wastewater treatment system depends on the construction and operation cost, the area demand and the required quality of effluent.

Ultrasound-induced inactivation of gram-negative and gram-positive bacteria in secondary treated municipal wastewater.

The effect of 24kHz, high energy ultrasound in the presence and absence of titanium dioxide particles on the destruction of different bacteria groups was studied. Applying a total of 1500W/L for 60min (this corresponds to 5400kJ/L specific nominal energy), the mean destruction of gram-negative bacteria such as total coliforms, faecal coliforms and Pseudomonas spp. was 99.5%, 99.2% and 99.7%, respectively. More recalcitrant to sonolytic inactivation were the gram-positive bacteria Clostridium perfringens and faecal streptococci with a mean removal of 66% and 84%, respectively. The presence of 5g/L TiO(2) generally enhanced the destruction of gram-negative bacteria, yielding three to five logs reduction. On the other hand, the relatively weak sonochemical inactivation of gram-positive bacteria was only slightly affected by the presence of solid particles. Inactivation was found to follow first-order kinetics regarding bacteria population and was not affected significantly by the wastewater quality. Ultrasound irradiation at 4000kJ/L specific nominal energy and in the presence of 5g/L TiO(2) achieved less than 10(3) CFU/100mL total coliforms, thus meeting USEPA quality standards for wastewater reuse.

Oil refinery sludge and green waste simulated windrow composting.

Oil refinery sludge (ORS) was mixed with shredded green wastes (GW) at ratios of 1:1 v/v (RI) and 1:3 v/v (RII). The mixtures, of approximately volumes of 1,020 l and 990 l respectively, were introduced in metal cubic containers of 1.0 m(3) volume, opened at the top and with small holes punctured in the bottom and the side. The containers were additionally insulated with a layer of rockwool (20 mm). The boxes were emptied, the mixtures were turned and water was added occasionally, in one to two weeks intervals, simulating a windrow composting system. Temperature, physiochemical characteristics, mineral oil and grease (MOG) concentration, polycyclic aromatic hydrocarbons (PAHs) concentration, carbon dioxide emission, methane emission and microorganisms presence were recorded either daily or every time the mixtures were turned, for a period of 120 days. RII recorded temperatures as high as 62 degrees C, reaching 56 degrees C in Day 6 and retained temperatures above 50 degrees C for more than 40 days. RI recorded its highest temperature of 53 degrees C in Day 77. The reason why the two mixtures behaved so differently can be explained by: (i) extended co-digestion phenomena by the microorganisms decomposing the GW in RII, (ii) toxic effect of ORS in RI due to the far larger amounts used (840 kg in RI in comparison with the 460 kg in RII). After Day 36 temperature increased gradually in RI and MOG and PAHs reduction was first noted. At the end of the experiment MOG concentration in RI was 57.2 mg/kg dry weight (dw) (52.1% reduction) where in RII was 34.3 mg/kg dw (62.1% reduction). Emissions of methane and carbon dioxide support the concept of the toxic effect and the delay ignition of the decomposing process in RI. In total, CO(2) and CH(4) emissions from RI were recorded to be 30.8 kg and 18.5 g, respectively, where from RII 59.6 kg of CO(2) and 6.4 g of CH(4) were emitted. An effort was made to determine the effect of temperature alone (as an abiotic treating parameter) in both mixtures. It can be supported that about least 15% of the MOG and PAHs removal.

Constructed wetlands treating highway runoff in the central Mediterranean region.

Two free water surface (FWS) and two subsurface flow (SSF) pilot-size constructed wetlands treating highway runoff (HRO) were monitored over a period of two years (September 2005-August 2007). One FWS and one SSF were designed with a hydraulic retention time (HRT) of 12h, named FWS12 and SSF12, respectively, with each one capable of treating a maximum HRO of 12.6 m(3) d(-1). The other couple, named FWS24 and SSF24, respectively, was designed with an HRT of 24h, with each receiving a maximum HRO of 6.3 m(3) d(-1). The influent flowed from a highway section with a total surface 2752 m(2) on the island of Crete, Greece, in the heart of the South-Central Mediterranean region. Influent and effluent were monitored for COD, TSS, total N (TN), NO(3)(-) and total P (TP) concentrations. Furthermore, removal efficiencies were examined for heavy metals (Cu, Ni, Pb, Zn) for both years, while polycyclic aromatic compounds (PAHs) were examined for the period between September 2006 and August 2007. The influent had a two-year average COD value of 101 mg l(-1), whereas the mean values for TSS, TN, N-NO(3)(-) and TP were 203, 4.30, 1.25 and 4.17 mg l(-1), respectively. For Cu, Ni, Pb and Zn the respective two-year mean influent concentrations were 56, 114, 49 and 250 microg l(-1). Mean concentration of total PAHs in runoff (summation operator PAHs, 16 compounds) were 12.01 microg l(-1). The performance among the four beds was not significantly different according to ANOVA analysis followed by Tukey test (at p<0.05) for almost all the above physicochemical parameters, suggesting that all systems performed in a similar way. All studied systems, achieved a mean of two-year removal efficiencies of 47% for COD, 89% for TSS, 49% for TN, 58% for N-NO(3)(-), 60% for TP, 47% for Cu, 23% for Ni, 33% for Pb, 61% for Zn and 59% for summation operator PAHs (16 compounds).

The effect of pharmaceuticals on the kinetics of methanogenesis and acetogenesis.

In this study, the widely used anaerobic digestion model (ADM1) was used in order to simulate the inhibition of three pharmaceuticals, propranolol hydrochloride, ofloxacin and diclofenac sodium, on two groups of microorganisms, acetogens and acetoclastic methanogens, the most sensitive microorganisms groups involved in the anaerobic digestion process. The specific maximum consumption rate and saturation constant of acetate and propionate degraders were estimated through fitting the model to experimental data taken from continuous and batch experiments. A modified non-competitive inhibition function was used, and the inhibition constants were estimated using data from Batch experiments conducted at various concentrations of pharmaceuticals using enriched cultures with propionate and acetate degraders. It was found that propranolol hydrochloride was the most inhibitory pharmaceutical to both microorganisms groups.

Simulation of DEHP biodegradation and sorption during the anaerobic digestion of secondary sludge.

Di-ethylhexyl phthalate (DEHP) has commonly been found in the sludge of municipal wastewater treatment plants especially during anaerobic processing. It is slowly biodegradable under anaerobic conditions. Due to its high hydrophobicity, sorption-desorption processes can be rate-limiting for the compound biodegradation. In this study, the anaerobic biodegradation of DEHP was investigated through batch kinetic experiments and dynamic transitions of a continuous stirred tank reactor (CSTR) fed with secondary sludge contaminated with DEHP. A widely accepted model (ADM1) was used to fit the anaerobic digestion of secondary sludge and was properly extended to account for DEHP removal, in which mass transfer processes are also involved. It was shown that DEHP removal was limited by the transfer of DEHP within the solid fraction. The criterion selected for the distinction of the two sites was whether the compound sorbed in those sites was bioavailable for biodegradation or not. Thus, the aqueous phase and the surface of the biosolids were considered as suitable sites for the compound to be bioavailable and the main bulk of the solid matrix was regarded as sites, where the compound remains "protected" against biodegradation. The model, fitted to the batch experimental data, was able to predict DEHP removal in the CSTR operated at various HRTs.

On the occasional biodegradation of pharmaceuticals in the activated sludge process: the example of the antibiotic sulfamethoxazole.

Sulfamethoxazole, a common antibiotic, was found to be biodegradable under aerobic conditions. The fate of sulfamethoxazole in the activated sludge process was studied using a Sequencing Batch Reactor (SBR). Aerobic biomass was acclimated to sulfamethoxazole and a series of kinetic experiments were conducted to investigate the impact of other carbon and nitrogen sources on the degradation of the antibiotic. It was found that sulfamethoxazole serves both as carbon and nitrogen source for the enriched consortium. It was degraded whenever there was a depletion of carbon or nitrogen or both in the feeding medium, while in the presence of acetate and ammonium nitrogen (alternative carbon and nitrogen sources, respectively), sulfamethoxazole remained intact.

Removal of phenolics in olive mill wastewaters using the white-rot fungus Pleurotus ostreatus.

Olive mill wastewaters (OMW) present a major environmental problem. The large amounts generated, combined with the high phenols and chemical oxygen demand concentrations, are the main difficulties in finding a solution for the management of these wastewaters, which are dangerous for the environment. The phenols, which are contained in the OMW have a structure similar to lignin, which makes them difficult to biodegrade. Lignin can be degraded only by a few microorganisms, such as "white-rot" basidiomycete, which produce manganese (MnPs) and lignin peroxidases (LiPs) and laccases that are responsible for the oxidisation of lignin compounds. The capability of Pleurotus ostreatus to degrade phenols of OMW in different conditions such as in sterilized and thermally processed (at 100 degrees C) wastewater, with and without dilution, is investigated in this work. According to the experimental results P. ostreatus removed phenols from the culture medium, under all different conditions that were examined. The degradation of phenols reached up to 78.3% for the sterilized and 50% diluted OMW, 66.7% and 64.7% for the thermally processed OMW, with and without dilution, respectively. The effect of pre-treatment of OMW on the performance of anaerobic digestion is also assessed, as methanogenic bacteria are seriously affected by the presence of phenol compounds. The pre-treated wastewater was shown to be more amenable to a subsequent anaerobic digestion.