Bio-degradation of olive mill wastewater sludge by its co-composting with agricultural wastes

The use of maize straw (MS) or cotton waste (CW) as bulking agents in the composting of olive mill wastewater (OMW) sludge was compared by studying the organic matter (OM) mineralisation and humification processes during composting and the characteristics of the end products. Both composts were prepared in a pilot-plant using the Rutgers static-pile system. The use of CW instead of MS to compost OMW sludge extended both the thermophilic and bio-oxidative phases of the process, with higher degradation of polymers (mainly lignin and cellulose), a greater formation of nitrates, higher total nitrogen losses and a lower biological nitrogen fixation. The CW produced a compost with a more stabilised OM and more highly polymerised humic-like substances. In the pile with CW and OMW sludge, OM losses followed a first-order kinetic equation, due to OM degradation being greater at the beginning of the composting and remaining almost constant until the end of the process. However, in the pile with MS and OMW sludge this parameter followed a zero-order kinetic equation, since OM degraded throughout the process. The germination index indicated the reduction of phytotoxicity during composting.     

Novel static composting method for bioremediation of olive mill waste

This paper presents results obtained on the evaluation of static composting process aimed at bioremediation of the hazardous solid olive mill waste (OMW). The static composting process carried out in gas-permeable polyethylene bags followed the fluctuating temperature and oxygen profiles similar to those seen in aerated composting systems. Static composting resulted in apparent increases and decreases in values for total nitrogen and C:N ratios respectively during the process. The amount of nitrogen (>3%) in the composting end product was in agreement with the Italian legislation (Decreto Legislativo 29 aprile 2010, n. 75) specification for nitrogen fertilizer. A gradual decrease in polyphenols during the storage of compost resulted in a non-phytotoxic composted organic matter high in humic substances. Different respirometric tests also stated high biological stability of the end compost product.     

Chemical properties and hydrolytic enzyme activities for the characterisation of two-phase olive mill wastes composting

Two-phase olive mill waste (TPOMW) is a semisolid sludge generated during the extraction of olive oil by the two-phase centrifugation system. Among all the available disposal options, composting is gaining interest as a sustainable strategy to recycle TPOMW for agricultural purposes. The quality of compost for agronomical use depends on the degree of organic matter stabilization, but despite several studies on the topic, there is not a single method available which alone can give a certain indication of compost stability. In addition, information on the biological and biochemical properties, including the enzymatic activity (EA) of compost, is rare. The aim of this work was to investigate the suitability of some enzymatic activities (beta-glucosidase, arylsulphatase, acid-phosphatase, alkaline-phosphatase, urease and fluorescein diacetate hydrolysis (FDA)) as parameters to evaluate organic matter stability during the composting of TPOMW. These enzymatic indices were also compared to conventional stability indices. For this purpose two composting piles were prepared by mixing TPOMW with sheep manure and grape stalks in different proportions, with forced aeration and occasional turnings. The composting of TPOMW followed the common pattern reported previously for this kind of material with a reduction of 40-50% of organic matter, a gradual increase in pH, disappearance of phytotoxicity and formation of humic-like C. All EA increased during composting except acid-phosphatase. Significant correlations were found between EA and some important conventional stability indices indicating that EA can be a simple and reliable tool to determine the degree of stability of TPOMW composts.     

Two-phase olive mill waste composting: enhancement of the composting rate and compost quality by grape stalks addition

Two-phase olive mill waste (TPOMW) is a semisolid sludge generated by the olive oil industry. Its recycling as a soil amendment, either unprocessed or composted, is being promoted as a beneficial agricultural practice in the Mediterranean area. One of the major difficulties when composting TPOMW is the compaction of the material due to its dough-like texture, which leads to an inadequate aeration. For this reason, the addition of bulking agents is particularly important to attain a proper composting process. In this study we followed the evolution of two composting mixtures (A and B) prepared by mixing equal amounts of TPOMW and sheep litter (SL) (in a dry weight basis). In pile B grape stalks (GS) were added (10% dry weight) as bulking agent to study their effect on the development of the composting process and the final compost quality. The incorporation of grape stalks to the composting mixture changed the organic matter (OM) degradation dynamics and notably reduced the total amount of lixiviates. The evolution of several maturation indices (C/N, germination index, water soluble carbon, humification indices, C/N in the leachates) showed a faster and improved composting process when GS were added. Moreover, chemical (NH₄ ⁺, NO₃ ⁻, cation exchange capacity, macro and micronutrients, heavy metals) and physical properties (bulk and real densities, air content, total water holding capacity, porosity) of the final composts were analysed and confirmed the superior quality of the compost where GS were added.     

Composting of olive leaves and pomace from a three-phase olive mill plant

The composting of olive leaves and olive pomace from a three-phase olive mill was tested as a method for solid waste reuse. The process was carried out using a compost windrow and mixing olive leaves and pomace at a ratio of 1:2. Compost was retained in the windrow for 60 days during which thermophilic temperatures developed for the first 40 days. The compost was then placed into a closed area to mature for another 60 days. The final product proved to be high quality amendment with C/N 27.1 and high nutrient concentrations (N, 1.79%; P, 0.17%; K, 4.97%; Na, 2.8%). Mature compost presented the highest germination index (198%) reported to date, as the germination index in the majority of previous studies is under 80%. Furthermore, tests revealed that addition of 31.5 tons of compost per ha, could increase lettuce yield by 145%.     

五氯酚在稻田中的降解动态及生物有效性

利用江西鹰潭红壤生态实验站的长期施肥定位试验,采用田间微域研究了五氯酚(pentachlorophenol, PCP)在红壤性水稻田生态系统中的降解动态和稻谷的富集特征。四种长期施肥处理包括:未施肥(对照,CK)、施尿素(N)、施有机肥(OM)以及施有机肥+尿素(N+OM)。结果表明,长期施用OM或N+OM能显著增加土壤微生物活性。PCP在土壤-水稻生态系统中的降解遵循一级动力学方程,在CK、N、OM 和 N+OM 4 种处理土壤中降解半衰期分别为 27.7、35.2、24.8、22.4 d。表明长期施用OM或N+OM能加速PCP降解,而长期施用N抑制PCP降解。土壤中PCP(初始浓度85 mg/kg)显著减少水稻茎和稻谷生物量,但是对水稻根生物量并没有显著影响。在4种处理中水稻稻谷中PCP含量并没有显著差异,且稻谷的生物富集系数均小于0.01。PCP虽然在土壤-水稻生态系统中的降解半衰期较短,但是仍可以在水稻稻谷中有一定的生物富集,潜在的食品安全风险依然存在。     

Biodegradation of olive husk mixed with other agricultural wastes

In this study, the evolution of the most important parameters (temperature, pH, electrical conductivity, total organic carbon, total nitrogen, and C/N ratio) describing the composting process of olive oil husk with other organic wastes was investigated. Four windrows for obtaining two mixed wastes composts (MWCs) and two green wastes composts (GWCs) were prepared.     

Ruminal degradability and in vitro intestinal digestibility of sunflower meal and in vitro digestibility of olive by-products supplemented with urea or sunflower meal: Comparison between goats and sheep

The in vitro digestibility of two-stage dried olive cake (TSDOC) and olive leaves (OL) unsupplemented or supplemented with increasing amounts of urea (U) or sunflower meal (SM) (0, 1.5, 2 and 2.5 g/100 g organic matter (OM) of the by-product) was determined. Chemical and amino acid composition, in vitro digestibility, in situ rumen degradability of crude protein and amino acids, and in situ–in vitro intestinal digestibility of SM CP and amino acids was determined. The in sacco rumen degradability and in vitro intestinal availability of CP and individual amino acids were also determined. Results obtained in Granadina goats and Segureña wethers were compared. SM provides arginine, glycine and aspartic and glutamic acids. The addition of increasing amounts of U or SM improved (P<0.001) the IVDMD and IVOMD of both TSDOC and OL. There was no effect (P>0.05) of the rumen inoculum origin on in vitro TSDOC digestibility. In contrast, values for OL were higher (P<0.001) for goats versus sheep. In sacco ruminal CP degradability of SM was relatively high, and similar in sheep and goats (ED=0.78 and 0.75 for sheep and goats). Individual amino acid ruminal degradability had different values, being lowest for methionine, leucine, proline, tyrosine and cysteine. Values obtained for individual amino acids differed from those of CP. Apparent intestinal digestibility of undegraded protein (AIDUP) of SM was high (0.86 and 0.98, respectively, for sheep and goats). The intestinally absorbable protein (IADP) was low (18.9 and 24.0 for sheep and goats, respectively). Results indicate that goats and sheep have the same capacity for TSDOC digestion, but goats showed a better capacity than sheep for OL utilisation. Although the amino acids supply to the intestine from SM is not important it could be a good supplement for low degradable protein feedstuffs such as TSDOC and OL.     

Monitoring of green waste composting process based on redox potential

Among compostable matrices, green wastes represent a significant fraction which can be used as an amendment after composting. Several indicators, e.g. C(HA)/C(FA) or C/N ratios give information on evolution of the organic matrix during composting. However, measurement of these parameters is complex and requires laboratory conditions. The aim of this study was to propose on site easy-to-measure parameters to monitor composting process, such as redox potential (Eh), related to complex indices such as C(HA)/C(FA), C/N, A(210 nm)/A(280 nm), NH(4)(+)/NO(3)(-) ratios, and total organic matter (OM). Windrows were consisting in a mixture of green wastes such as palm, olive, cypress, pine, mimosa, and bay residues. By using covariance analysis, an opposite correlation between Eh and C(HA)/C(FA) ratio was found. Linear regression of this parameter with Eh was chosen to monitor the composting process. Therefore, Eh can be used to monitor green wastes composting.     

Phytotoxicity of olive tree leaf compost in relation to the organic acid concentration

Olive tree leaves are one of the most abundant organic residues on the island of Crete. The objective of this study was to investigate the changes of phytotoxicity of olive tree leaves during the composting process in piles and correlate them with the changes of organic acid concentration. For this purpose, four piles were established with urea or ammonium nitrate as the nitrogen source. The piles were turned and sampled every 8 or 10 days. The organic compounds were extracted by ether from water extracts of the olive tree leaf samples and redissolved in water. The phytotoxicity of the ethersoluble organic compounds was determined by their inhibitory effect on the germination of lettuce seeds and was compared with the phytotoxicity of pure organic acids and sterile water. It was found that the organic acid concentration increased for approximately 2 weeks during the composting process and then decreased progressively. The phytotoxicity of both the ether-soluble organic extracts and the control solutions correlated inversely with the organic acid concentrations. However, it was higher in the olive tree leaf extracts than in the control solutions of pure formic, acetic, benzoic, salicylic, or tannic acid. These findings indicate that the phytotoxity consists of organic acids different from the control acids tested and/or other organic compounds.     

Effects of olive mill wastewater addition in composting of agroindustrial and urban wastes

In order to study the suitability of olive mill wastewater (OMW) for composting, thisliquid waste was added to two different mixtures of agroindustrial and urban wastesand the composting process was compared with two other piles of similar composition,but without OMW. These four piles were studied in a pilot plant using the Rutgers staticpile system. The addition of OMW produced a greater proportion of degradable organic matter or a higher degradation rate, higher electrical conductivity values, greater losses of total N and lower nitrification than in piles without OMW. Its addition also restricted the increase of the cation exchange capacity and provoked the appearance of phytotoxicity or a longer persistence of phytotoxicity. However, in general, all the composts showed increases in the cation exchange capacity, the percentage of humic acid-like carbon, the polymerisation ratio of these humic substances (which revealed that the organic matter had been humified during composting) and the germination index, the latter indicating the reduction of phytotoxicity during the process.     

Pile composting of two-phase centrifuged olive husk residues: technical solutions and quality of cured compost

The present work proposed an economically sustainable solution for composting olive humid husks (OHH) and leaves (OL) at a small/medium sized olive oil mill. We planned and set up a composting plant, the prototype taking the form of a simplified low-cost turning machine, and evaluated the use of an inoculum of one year-old composted humid husks (CHH) and sheep manure (SM) to facilitate the starting phase of the process. Trials were carried out using four piles under different experimental conditions (turnover, static, and type of inoculum). The best results were achieved with turnover and an inoculum that induced fast start-up and a correct evolution of the composting process. The final product was a hygienically clean, cured compost.     

Dynamics of pruning waste and spent horse litter co-composting as determined by chemical parameters

Co-composting of pruning waste and horse manure was monitored by different parameters. A windrow composting pile, having the dimensions 2.5m (height) x 30m (length) was established. The maturation of pruning waste and horse manure compost was accompanied by a decline in NH(4)(+)-N concentration, water soluble C and an increase in NO(3)(-)-N content. Organic matter (OM) content during composting followed a first-order kinetic equation. This result was in agreement with the microbiological activity measured by the CO(2) respiration during the process. The correlation at a high level of probability found between the OM loss and CO(2) evolution showed that both parameters could be used to indicate the degree of OM degradation that is the maturity and stability phases of the compost studied. Humification parameters data from the organic matter fractionation did not show a clear tendency during the composting time, suggesting that these parameters are not suitable for evaluating the dynamics of the process.     

Optimizing composting parameters for nitrogen conservation in composting

A central composite experimental design was used to investigate the influence of environmental composting parameters (moisture, aeration, particle size and time) for legume trimming residues, used on soil restoration, on the properties of products obtained (organic matter, Kjeldahl-N, C/N ratio and nitrogen losses (N-losses)) in order to determine the best composting conditions. A second-order polynomial model consisting of four independent process variables was found to accurately describe (the differences between the experimental values and those estimated by using the equations never exceeded 10% of the former) the composting process. Results of the experiment showed that compost with acceptably chemical properties (OM, 85%; Kjeldahl-N, 3.2%), high degradation and minimum N-losses entails operating at high operation time (78 days), low particle size (1cm), medium moisture content (40%) and medium to low aeration level (0.2-0.4 l air/min kg).     

Effect of polyethylene glycol,urea and sunflower meal on olive (Olea europaea var. europaea) leaf fermentation in continuous fermentors

A continuous culture system, inoculated with rumen liquor from goats or sheep, was used to study fermentation characteristics of olive leaves (OL). The effects of adding polyethylene glycol (PEG 4000 MW; 0, 2 or 20 g/100 g OL) and/or supplementing with urea (U) or sunflower meal (SM) (1.0 g N/100 g OM) were also studied. Olive leaf fermentation promoted low VFA production (35.2 mmol/d), predominantly of acetic acid, and low efficiency of VFA production (4.91 mol/kg digestible carbohydrates, DCHO). Both values increased with N supplementation, but effects of PEG were variable. No differences ascribed to the rumen inoculum origin were observed. The ammonia N concentration was increased only by supplementation with U. Total and amino acid N output was low and increased with N addition, but it was not affected by PEG treatment. No differences ascribed to the inoculum origin were observed concerning microbial N production rate or efficiency (g N/kg DCHO). There was no clear difference between sources of supplementary N regarding bacterial protein synthesis. On the basis of PEG results, the effect of tannins on OL fermentation was not important.     

Anaerobic digestion of alcohol sulfate (anionic surfactant) rich wastewater--batch experiments. Part II: influence of the hydrophobic chain length

The mineralisation and the humification of organic matter (OM) in sterile horticultural plant wastes inoculated with Coriolus versicolor or Phanerochaete flavido-alba was investigated under different aeration rates in order to determine their efficacy as potential inoculants for composting. The change in elemental composition, lignin content and OM fractions was analysed during a 90-day incubation. Both fungi degraded 30% of lignin at low aeration rates. Different aeration rates led to significant changes in OM mineralisation induced by C. versicolor, but did not have noticeable effect on P. flavido-alba activity. The mineralisation was more effectively carried out by P. flavido-alba than by C. versicolor. Lignin degradation and the linked humification process were equally achieved by the two fungi and were enhanced in aerated conditions. The fungi analysed may facilitate the composting of lignocellulosic wastes by means of an increase in substrate bioavailability and OM humification.     

Bio-degradation of olive oil husks in composting aerated piles

In this study, the composting performance of two olive oil husk piles was compared using two different aeration processes: aeration by mechanical turning or by forced air-injection. The results showed that after the maturation phase both piles had a similar chemical composition and the same level of organic matter degradation (around 55%). However, the time necessary to reach the thermophilic phase was shorter for the turned pile (2 months in comparison to 3 months for the air-injected pile) and the humification degree achieved was slightly higher (94% versus 83%). Both piles showed the presence of an active microbial community, with an increase by 2-3 orders of magnitude in the number of cultured microbial colonies during the composting process. No significant difference in quantitative or qualitative terms was found in the microbial populations of both piles, nor was a clear succession between a mesophilic and a thermophilic population observed. In terms of industrial application, the mechanical turning process seems to be better since it is a lower energy and time consuming process.     

Microbial degradation and humification of the lawn care pesticide 2,4-dichlorophenoxyacetic acid during the composting of yard trimmings.

The fate of the widely used lawn care herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) during the composting of yard trimmings consisting of primarily leaves and grass is an important unexplored question. In this study, we determined the extent of 2,4-D mineralization, incorporation into humic matter, volatilization, and sorption during the composting of yard trimmings. Yard trimmings (2:1 [wt/wt] leaves-grass) were amended with 14C-ring-labeled 2,4-D (17 mg/kg of dry weight) and composted in a temperature-controlled laboratory scale compost system. During composting, thermophilic microbes were numerically dominant, reaching a maximum of 2 x 10(11)/g. At the end of composting, 46% of the organic matter (OM) present in the yard trimmings was lost and the compost was stable, with an oxygen uptake rate of 0.09 mg of O2 per g of OM per h, and was well humified (humification index, 0.39). Mineralization of the OM temporally paralleled mineralization of 2,4-D. In the final compost, 47% of the added 2,4-D carbon was mineralized, about 23% was complexed with high-molecular-weight humic acids, and about 20% was not extractable (humin fraction). Less than 1% of the added 14C was present in water expressed from the finished compost, suggesting a low potential for leaching of 2,4-D. Very little volatilization of 2,4-D occurred during composting. It is of interest that our results indicate active mineralization of 2,4-D at composting temperatures of 60 degrees C because microbial 2,4-D degradation at thermophilic temperatures has not been previously documented.     

Carbon mineralization and distribution of nutrients within different particle-size fractions of commercially produced olive mill pomace

Composting is a realistic option for disposal of olive mill pomace (OMP) by making it suitable as a soil amendment for organic farming. The chemical and physical characteristics and contribution of particle-size fractions to total nutrients and carbon mineralization of seven commercial composts of OMP (COMP) were investigated. Higher proportions of manure, co-composted with OMP, reduced the organic matter (OM), total carbon and C:N ratio of the product, but increased the content of nutrients and fine particles. The fine particles had higher nutrient contents, but less OM and carbon and, unlike larger particles, did not exhibit any phytotoxicity. Less than 1.5% of added carbon was mineralized in whole compost, but a lower rate was found with larger particles. Separation of COMP by particle size fractionation and application as a soil conditioner is recommended for better optimization of COMP with the <1 mm fraction providing the higher quality compost.     

Effect of bioaugmentation and nitrogen supplementation on composting of paddy straw

A composting experiment was conducted to evaluate the effect of a hyperlignocellulolytic fungal consortium and different nitrogen amendments on paddy straw composting in terms of changes in physicochemical and biological parameters. A fungal consortium comprising four lignocellulolytic mesophilic fungal cultures was used as inoculum for bioaugmentation of paddy straw in perforated pits. The comparative effect of farmyard manure (FYM), soybean trash, poultry litter and urea on the composting process was evaluated at monthly intervals in terms of physicochemical (pH, EC, available P, C:N ratio and humus content) and biological (enzymatic and microbial activity) parameters. The compost prepared from bioaugmented paddy straw composting mixture, with poultry manure as nitrogen supplement attained desirable C:N ratio in 1 month and displayed least phytotoxicity levels along with higher production of β-1,4-Exoglucanase. The combined activity of the autochthonous composting microbiota as well as the externally applied fungal inoculum accelerated the composting process of paddy straw. Supplementation of paddy straw with poultry manure in 8:1 ratio was identified as the best treatment to hasten the composting process. This study highlights the importance of application of fungal inoculum and an appropriate N-amendment such as poultry manure for preparation of compost using a substrate having high C:N ratio, such as paddy straw.