Composting and bioremediation process evaluation of wood waste materials generated from the construction and demolition industry

Poplar Sawdust Stack Self-Heating Properties and Variations of Internal Microbial Communities

The heat accumulation generated by microbial metabolic activities during the storage of the sawdust may lead to spontaneous combustion accidents. This paper studied the Critical Ambient Temperature (CAT) variation of poplar sawdust at different stack dimensions and investigated the physicochemical properties as well as microbial community dynamics during the self-heating process of poplar sawdust stacks. From the self-heating substances test experiments and Frank-Kamenetskii (FK) theory, it was found that the CAT of poplar sawdust stacks would decrease from 158.27 °C to 102.46 °C with the increase of stack size from 0.1 m to 3.2 m. From the sawdust stack self-heating experiments, microbial metabolic activities were enhanced with the increasing moisture content (by watering) and oxygen (by turning over), which led to a remarkable increase of the sawdust stack temperature and the rapid decomposition of biochemical components (especially cellulose and hemicellulose). From the microbiological community analysis, at the thermophilic stage (around 60 °C, large amounts of heat release in compost bin), the existence of thermostable bacteria (such as Brevibacillus thermoruber, Bacillus thermoamylovorans and Paenibacillus barengoltzii belonging to Firmicutes) played an important role in degrading organic substances. The heat generated by the microbial metabolic activities might lead to spontaneous combustion eventually if sawdust stack is large enough. Therefore, the sawdust should be stacked in a cool and dry area while avoiding large amounts of storage in high humidity environments.

Organic soil additives for the remediation of cadmium contaminated soils and their impact on the soil-plant system: A review

Immobilization is among the most-suitable strategies to remediate cadmium (Cd) contaminated sites. Organic additives (OAs) have emerged as highly efficient and environment-friendly immobilizers to eradicate Cd contamination in a wide range of environments. This review article is intended to critically illustrate the role of different OAs in Cd immobilization and to highlight the key findings in this context. Owing to the unique structural features (high surface area, cation exchange capacity (CEC), presence of many functional groups), OAs have shown strong capability to remediate Cd polluted soils by adsorption, electrostatic interaction, complexation and precipitation. Research data is compiled about the efficiency of different OAs (bio-waste, biochar, activated carbon, composts, manure, and plant residues) applied alone or in combination with other amendments in stabilization and renovation of contaminated sites. In addition to their role in remediation, OAs are widely advocated for being classical sources of essential plant nutrients and as agents to improve the soil health and quality which has also been focused in this review. OAs may contain considerable amounts of metals and therefore it becomes essential to assess their final contribution. Elimination of Cd contamination is essential to attenuate the contaminant effect and to produce the safe food. Therefore, deployment of environment-friendly remediation strategies (alone or in combination with other suitable technologies) should be adopted especially at early stages of contamination.

Effect of initial material bulk density and easily-degraded organic matter content on temperature changes during composting of cucumber stalk

To inactivate the potentially pathogenic microorganisms and safely utilize vegetable waste compost, ultra-high temperatures (>70°C) should be maintained during the composting without having an inhibitory effect on maturity. This study investigated the influence of bulk density (part 1) and easily-degraded organic matter content (EDOMC, part 2) on temperature evolution during vegetable waste composting: Part 1: corn straw with different particle sizes was used to achieve different bulk densities in the composting material (BD1-BD3); Part 2: partial or total substitution of the corn straw by corn starch was carried out to obtain different EDOMC (ED1-ED4). The composting experiments were conducted in a lab-scale reactor (1.75kg material) and lasted for 30d. Temperature and CO₂ emission were recorded daily, and the organic matter, lignocellulose, microbial activity, germination index (GI) and C/N of the samples were measured at different stages. The highest temperature (65.7°C) in part 1 occurred in the treatment with the bulk density of 0.35g/cm³, which also had the longest thermophilic phase. Bulk density was found to seriously influence the utilization efficiency of O₂ and heat transfer through materials, rather than heat production from organic matter degradation. In experiment part 2, the highest temperature was obtained with EDOMC of 45% (71.4°C). Therefore, adjusting the bulk density to 0.35g/cm³ and the easily-degraded organic matter content of the initial material to 45% was the best combination for reaching temperatures above 70°C during composting, with no inhibitory effect on the maturity of the compost product.

Using polyethylene sleeves with forced aeration for composting olive mill wastewater pre-absorbed by vegetative waste

Composting in closed polyethylene sleeves with forced aeration may minimize odor emissions, vectors attraction and leachates associated with open windrows. The present study demonstrates the use of this system for composting olive mill wastewater (OMW), the undesired stream associated with the olive milling industry. A polyethylene sleeve of 1.5-m diameter and ca. 20-m long was packed with shredded municipal green waste which was pre-soaked in OMW for 72 h. Process conditions were controlled by means of a programmable logic controller (PLC) equipped with temperature and oxygen sensors. Thermophilic temperatures (>45 °C) were maintained for one month followed by temperatures in the range of 30-40 °C, ca. 20 °C above ambient temperature, for a period of 3.5 months. Oxygen levels were controlled and the system was kept aerobic. Water content gradually decreased with sufficient levels for efficient composting. The finished compost was non-phytotoxic to Cress (Lepidium sativum L.) in a lab bioassay. It was also found suitable as an ingredient in peat, tuff, and coir based growing media, evaluated by plant growth tests with basil and ornamental plants. The viability of this approach for disposing off OMW is much dependent on the liquid absorption capacity of the vegetative waste.

Composting municipal biosolids in polyethylene sleeves with forced aeration: Process control, air emissions, sanitary and agronomic aspects

Composting in polyethylene sleeves with forced aeration may minimize odor emissions, vectors attraction and leachates associated with open windrows. A disadvantage of this technology is the lack of mixing during composting, potentially leading to non-uniform products. In two pilot experiments using biosolids and green waste (1:1; v:v), thermophilic conditions (>45°C) were maintained for two months, with successful control of oxygen levels and sufficient moisture. Emitted odors declined from 1.5-3.8×10⁵ to 5.9×10³-2.3×10⁴ odor units m^-3-air in the first 3weeks of the process, emphasizing the need of odor control primarily during this period. Therefore, composting might be managed in two phases: (i) a closed sleeve for 6-8weeks during which the odor is treated; (ii) an open pile (odor control is not necessary). Reduction of salmonella, E. coli and coliforms was effective initially, meeting the standards of "Class A" biosolids; however, total and fecal coliforms density increased after opening the second sleeve and exceeded the standard of 1000 most probable number (MPN) per g dry matter. Compost maturity was achieved in the open piles following the two sleeves and the final compost was non-phytotoxic and beneficial as a soil additive.

Evaluating the performance and intellectual structure of construction and demolition waste research during 2000-2016

Construction and demolition (C&D) waste diminishes scarce land resources and endangers human health and the surrounding environment. Quantitative and visualized analysis was conducted to evaluate worldwide scientific research output on C&D waste from 2000 to 2016. The related information of 857 publications was collected from SCI-Expanded database and statistically analyzed. The number of documents about C&D waste presented a general growth during the last 17 years. Construction and Building Materials publication ranked first in the most productive journals. China and Spain acted as dominated roles comparing to other countries, and Hong Kong Polytechnic University was the institution with the largest amount of C&D waste research. Recycled aggregates, sustainable C&D waste management, and the rewarding program and commerce system were the hottest topics during 2000-2016 and in the near future according to the intellectual structure analysis.

Polycyclic aromatic hydrocarbons degradation and microbial community shifts during co-composting of creosote-treated wood

The feasibility of decontaminating creosote-treated wood (CTW) by co-composting with agricultural wastes was investigated using two bulking agents, grass cuttings (GC) and broiler litter (BL), each employed at a 1:1 ratio with the matrix. The initial concentration of total polycyclic aromatic hydrocarbons (PAHs) in CTW (26,500 mg kg(-1)) was reduced to 3 and 19% after 240 d in GC and BL compost, respectively. PAH degradation exceeded the predicted bioaccesible threshold, estimated through sequential supercritical CO2 extraction, together with significant detoxification, assessed by contact tests using Vibrio fisheri and Hordeum vulgare. GC composting was characterized by high microbial biomass growth in the early phases, as suggested by phospholipid fatty acid analyses. Based on the 454-pyrosequencing results, fungi (mostly Saccharomycetales) constituted an important portion of the microbial community, and bacteria were characterized by rapid shifts (from Firmicutes (Bacilli) and Actinobacteria to Proteobacteria). However, during BL composting, larger amounts of prokaryotic and eukaryotic PLFA markers were observed during the cooling and maturation phases, which were dominated by Proteobacteria and fungi belonging to the Ascomycota and those putatively related to the Glomeromycota. This work reports the first in-depth analysis of the chemical and microbiological processes that occur during the co-composting of a PAH-contaminated matrix.

Co-composting of Beef Cattle Feedlot Manure with Construction and Demolition Waste

With increased availability of dried distillers' grains with solubles (DDGS) as cattle feed and the need to recycle organic wastes, this research investigated the feasibility of co-composting DDGS cattle feedlot manure with construction and demolition (C&D) waste. Manure was collected from cattle fed a typical western Canadian finishing diet (CK) of 860 g rolled barley ( L.) grain, 100 g barley silage, and 40 g vitamin and mineral supplement kg dry matter (DM) and from cattle fed the same diet but (DG manure) with 300 g kg DM barley grain being replaced by DDGS. The CK and DG manures were co-composted with and without C&D waste in 13 m bins. Compost materials were turned on Days 14, 37, and 64, and terminated on Day 99. Adding C&D waste led to higher compost temperatures (0.4 to 16.3°C, average 7.2°C) than manure alone. Final composts had similar total C, total N, C/N ratios, and water-extractable K, Mg, and NO content across all treatments. However, adding C&D waste increased δC, δN, water-extractable SO, and Ca contents and decreased pH, total P (TP), water-extractable C, N, and P and most volatile fatty acids (VFA). The higher C&D compost temperatures should reduce pathogens while reduced VFA content should reduce odors. When using the final compost product, the increased SO and reduced TP and available N and P content in C&D waste compost should be taken into consideration. Increased S content in C&D compost may be beneficial for some crops grown on S-deficient soils.

Dynamics of microbial communities related to biochemical parameters during vermicomposting and maturation of agroindustrial lignocellulose wastes

Scarce information is available on the changes in abundance of microbial taxa during vermicomposting. Quantitative PCR and DGGE analysis were used to monitor variations in the microbial structure, relative abundance of four bacterial classes and fungi over the vermicomposting and maturation period of wet olive cake (O) and vine shoots (W). Multivariate correlation analysis between microbial structure and abundance, earthworm biomass and enzyme activities revealed similar and divergent interactions in both processes. Although Eisenia fetida development was different, significant correlations were found with β-glucosidase activity and with bacterial and fungal structure. In the vermicomposting period of O and W, a decline was found in bacteria (94% and 77%), fungi (93% and 94%), and Gammaproteobacteria (56% and 71%) but an increase in Betaproteobacteria and Actinobacteria (62-79%). Alphaproteobacteria increased only in O (26%). Despite the different initial lignocellulose wastes, the mature vermicomposts were similar in microbial and biochemical properties.

Emerging technologies in bioremediation: constraints and opportunities

Intensive industrialisation, inadequate disposal, large-scale manufacturing activities and leaks of organic compounds have resulted in long-term persistent sources of contamination of soil and groundwater. This is a major environmental, policy and health issue because of adverse effects of contaminants on humans and ecosystems. Current technologies for remediation of contaminated sites include chemical and physical remediation, incineration and bioremediation. With recent advancements, bioremediation offers an environmentally friendly, economically viable and socially acceptable option to remove contaminants from the environment. Three main approaches of bioremediation include use of microbes, plants and enzymatic remediation. All three approaches have been used with some success but are limited by various confounding factors. In this paper, we provide a brief overview on the approaches, their limitations and highlights emerging technologies that have potential to revolutionise the enzymatic and plant-based bioremediation approaches.

Enhancement of wood waste decomposition by microbial inoculation prior to vermicomposting

To investigate the feasibility of microbial pre-decomposition of timber wastes to quality production of vermicompost with higher agronomic value, timber wastes were inoculated with different combinations of the fungi Phanerochete chrysosporium, Trichoderma reesei, Aspergillus niger and the bacteria Azotobacter chroococcum (MTCC 3853) and Bacillus cereus (MTCC 4079) and incubated at 28-30 °C in a mechanical composter. The inoculation enhanced the degradation of timber wastes, increased total nitrogen and improved the quality and enhanced production of vermicompost generated with the native earthworm Drawida willsi Michelsen. Total nitrogen increased from 0.16% to 1.52% and total organic carbon (TOC) decreased from 42% to 13%. Out of 10 microbial combinations tested for pre-decomposition, the combination of P. chrysosporium+T. reesei was found best in terms of ligno-cellulosic decomposition, and P. chrysosporium+A. niger+B. cereus with respect of cast output. The study shows that microbial pre-decomposition of timber wastes to produce quality vermicompost is a feasible technology.

Evaluation of the potential of applying composting/bioremediation techniques to wastes generated within the construction industry

The objective of the present study was to evaluate the viability of reducing landfill requirements to satisfy EC Landfill Directive requirements by applying composting/bioremediation techniques to the construction and demolition (C&D) industry waste stream at laboratory scale. The experimental study was carried out in nine test rigs to examine different wood mixtures; untreated timber, creosote treated timber and chromated copper arsenate (CCA) treated timber. Several experimental variables affecting the process were characterised and optimised. These include the best nitrogen additive and optimum moisture content required for composting. Poultry manure was found to be the best nitrogen additive. The optimum moisture content was decreased after the addition of poultry manure. The composting/bioremediation process was evaluated through monitoring the microbial activity, carbon dioxide emissions and toxicity examination of the composted product. A typical temperature profile suggested that untreated and CCA treated mix could be classified as hot composting whereas creosote treated mix could be classified as cold composting. The paper reports on the results obtained during this investigation.