Abstract
BackgroundPaper pulp wastewater resulting from alkaline extraction of wheat straw, known as black liquor, is very difficult to be treated and causes serious environmental problems due to its high pH value and chemical oxygen demand (COD) pollution load. Lignin, semicellulose and cellulose are the main contributors to the high COD values in black liquor. Very few microorganisms can survive in such harsh environments of the alkaline wheat straw black liquor. A naturally developed microbial community was found accidentally in a black liquor storing pool in a paper pulp mill of China. The community was effective in pH decreasing, color and COD removing from the high alkaline and high COD black liquor.FindingsThirty-eight strains of bacteria were isolated from the black liquor storing pool, and were grouped as eleven operational taxonomy units (OTUs) using random amplified polymorphic DNA-PCR profiles (RAPD). Eleven representative strains of each OTU, which were identified as genera of Halomonas and Bacillus, were used to construct a consortium to treat black liquor with a high pH value of 11.0 and very high COD pollution load of 142,600 mg l−1. After treatment by the constructed consortium, about 35.4% of color and 39,000 mg l−1 (27.3%) CODcr were removed and the pH decreased to 7.8. 16S rRNA gene polymerase chain reaction denaturant gradient gel electrophoresis (PCR-DGGE) and gas chromatography/mass spectrometry (GC/MS) analysis suggested a two-stage treatment mechanism to elucidate the interspecies collaboration: Halomonas isolates were important in the first stage to produce organic acids that contributed to the pH decline, while Bacillus isolates were involved in the degradation of lignin derivatives in the second stage under lower pH conditions.Conclusions/SignificanceTolerance to the high alkaline environment and good controllability of the simple consortium suggested that the constructed consortium has good potential for black liquor treatment. Facilitating the treatment process by the constructed consortium would provide a promising opportunity to reduce the pollution, as well as to save forest resources and add value to a waste product.
Highlights
Wood is almost as important to humanity as food, and the natural forests from which most of it is harvested from are of enormous environmental value [1]
Grouping and identification of isolates Thirty-eight strains of bacteria were isolated from the black liquor, and eleven different profiles were primarily grouped according to random amplified polymorphic DNA-Polymerase chain reaction (PCR) profiles (RAPD) analysis (Figure 1). 16S rRNA gene of one representative strain in every operational taxonomy unit (OTU) was sequenced and used for constructing the phylogenetic tree (Figure 2), and the eleven representative isolates were divided into two clusters
Alkaliphilic or halophilic microorganisms have been mainly isolated from ecological environments such as soda lakes, sea water, as well as the ones generated by industrial activities [21]
Summary
Wood is almost as important to humanity as food, and the natural forests from which most of it is harvested from are of enormous environmental value [1]. The alkaline wastewater from wheat straw generally has a high pH value from 11.0 to 13.0 and a very high pollution load with oxygen demand (COD) above 100,000 mg l21 [4], which is called black liquor due to the chromophores in lignin and its derivatives Discharge of such effluent into streams and rivers has caused many environmental problems, such as thermal impacts, slime growth, scum formation as well as loss of aesthetic beauty [5]. Paper pulp wastewater resulting from alkaline extraction of wheat straw, known as black liquor, is very difficult to be treated and causes serious environmental problems due to its high pH value and chemical oxygen demand (COD) pollution load. The community was effective in pH decreasing, color and COD removing from the high alkaline and high COD black liquor
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
