Locally produced lactic acid bacteria for pathogen inactivation and odor control in fecal sludge

Repurposing anaerobic digestate for economical biomanufacturing and water recovery

Due to mounting impacts of climate change, particularly increased incidence of drought, hence water scarcity, it has become imperative to develop new technologies for recovering water from nutrient-rich, water-replete effluents other than sewage. Notably, anaerobic digestate could be harnessed for the purpose of water recovery by repurposing digestate-borne minerals as nutrients in fermentative processes. The high concentrations of ammonium, phosphate, sulfate, and metals in anaerobic digestate are veritable microbial nutrients that could be harnessed for bio-production of bulk and specialty chemicals. Tethering nutrient sequestration from anaerobic digestate to bio-product accumulation offers promise for concomitant water recovery, bio-chemical production, and possible phosphate recovery. In this review, we explore the potential of anaerobic digestate as a nutrient source and as a buffering agent in fermentative production of glutamine, glutamate, fumarate, lactate, and succinate. Additionally, we discuss the potential of synthetic biology as a tool for enhancing nutrient removal from anaerobic digestate and for expanding the range of products derivable from digestate-based fermentations. Strategies that harness the nutrients in anaerobic digestate with bio-product accumulation and water recovery could have far-reaching implications on sustainable management of nutrient-rich manure, tannery, and fish processing effluents that also contain high amounts of water. KEY POINTS: • Anaerobic digestate may serve as a source of nutrients in fermentation. • Use of digestate in fermentation would lead to the recovery of valuable water.

Small-scale on-site treatment of fecal matter: comparison of treatments for resource recovery and sanitization

On-site small-scale sanitation is common in rural areas and areas without infrastructure, but the treatment of the collected fecal matter can be inefficient and is seldom directed to resource recovery. The aim of this study was to compare low-technology solutions such as composting and lactic acid fermentation (LAF) followed by vermicomposting in terms of treatment efficiency, potential human and environmental risks, and stabilization of the material for reuse in agriculture. A specific and novel focus of the study was the fate of native pharmaceutical compounds in the fecal matter. Composting, with and without the addition of biochar, was monitored by temperature and CO₂ production and compared with LAF. All treatments were run at three different ambient temperatures (7, 20, and 38°C) and followed by vermicomposting at room temperature. Materials resulting from composting and LAF were analyzed for fecal indicators, physicochemical characteristics, and residues of ten commonly used pharmaceuticals and compared to the initial substrate. Vermicomposting was used as secondary treatment and assessed by enumeration of Escherichia coli, worm density, and physicochemical characteristics. Composting at 38°C induced the highest microbial activity and resulted in better stability of the treated material, higher N content, lower numbers of fecal indicators, and less pharmaceutical compounds as compared to LAF. Even though analysis of pH after LAF suggested incomplete fermentation, E. coli cell numbers were significantly lower in all LAF treatments compared to composting at 7°C, and some of the anionic pharmaceutical compounds were detected in lower concentrations. The addition of approximately 5 vol % biochar to the composting did not yield significant differences in measured parameters. Vermicomposting further stabilized the material, and the treatments previously composted at 7°C and 20°C had the highest worm density. These results suggest that in small-scale decentralized sanitary facilities, the ambient temperatures can significantly influence the treatment and the options for safe reuse of the material.

Control of septage sanitization by limes and lactic acid fermentation

Considering low-cost and effective fecal sludge (FS) treatment alternatives is essential to avoid risk to human health and to ensure safe disposal in landfills and soils. This research assesses optimal pH adjustment of two techniques for sanitizing de-watered FS from a septic sewage-treatment plant. The preliminary analysis evaluated the efficiency of lactic acid fermentation (LAF) by two lactic acid strains: Lactobacillus casei and Lactobacillus acidophilus. The homofermentative strain was chosen to evaluate three supplementary sugars: smashed carrot, sugarcane-derived molasses, and anhydrous dextrose. Lime treatment was examined using two materials, CaO, 105% calcium carbonate equivalent (CCE)_, and Ca(OH)₂, 75% CCE. Four samples were retrieved from a passive thermal drying bed, two characterized by its available nutrient content; all samples were analyzed for the pathogenic profile, and total coliforms (TC) were selected as indicators. For LAF, an inoculating rate of Lactobacillus casei 10 g/100 g sludge was found effective in decreasing the pH below 4.0 after 30 days of fermentation, using 22% w/w dextrose/septage and 20% w/w molasses/septage, where molasses contains 20.7% of soluble sugars. In the case of lime treatment, the pH was fitted by a power-law relationship to the rate of lime applied in a septage with an initial pH lower than 7.0. A Langmuir type equation fitted better the liming of two septages with initial pHs above 7.0. The rate of lime CaO 10% w/w was observed to increase the pH above critical value, 12, after 1 h and 24 h. Analysis confirmed the total elimination of TC in samples with pH < 4.0 and pH > 12, contrasting the respective controls. Rates of CaO considering the initial pH of the FS are recommended in order to reach pH 12. Septage sanitization can be completed using either CaO or lactic acid fermentation with molasses; selecting the ideal method will rely on cost-benefit analysis. Sanitization can be considered as well to improve safety soil nutrient recycling practices.

Hierarchical Bayesian modeling for predictive environmental microbiology toward a safe use of human excreta: Systematic review and meta-analysis

The pathogen concentration in human excreta needs to be managed appropriately, but a predictive approach has yet to be implemented due to a lack of kinetics models for pathogen inactivation that are available under varied environmental conditions. Our goals were to develop inactivation kinetics models of microorganisms applicable under varied environmental conditions of excreta matrices and to identify the appropriate indicators that can be monitored during disinfection processes. We conducted a systematic review targeting previous studies that presented time-course decay of a microorganism and environmental conditions of matrices. Defined as a function of measurable factors including treatment time, pH, temperature, ammonia concentration and moisture content, the kinetic model parameters were statistically estimated using hierarchical Bayesian modeling. The inactivation kinetics models were constructed for Escherichia coli, Salmonella, Enterococcus, Ascaris eggs, bacteriophage MS2, enterobacteria phage phiX174 and adenovirus. The inactivation rates of a microorganism were predicted using the established model. Ascaris eggs were identified as the most tolerant microorganisms, followed by bacteriophage MS2 and Enterococcus. Ammonia concentration, temperature and moisture content were the critical factors for the Ascaris inactivation. Our model predictions coincided with the current WHO guidelines. The developed inactivation kinetics models enable us to predict microbial concentration in excreta matrices under varied environmental conditions, which is essential for microbiological risk management in emerging resource recovery practices from human excreta.

Bioleaching of heavy metals from wastewater sludge with the aim of land application

Presence of heavy metals in the wastewater sludge has greatly hindered sludge land application. Bioleaching has been developed for heavy metal removal from sludge. The pH of the sludge is declined by microorganisms with S or FeS as energy source. Sludge considered to be used in land is mainly due to its fertilizer values as it contains nitrogen, phosphorus, and potassium. Therefore, it is important to understand how the bioleaching would impact on sludge characterization. In addition, pathogens are great threat to human health. The ability of pathogen elimination of bioleaching is highly concerned. In this review, the major heavy metals in the sludge are summarized. The change of nitrogen, phosphorus, and potassium after bioleaching is stated. The pathogen elimination due to bioleaching has been discussed. The work has provided an insight of research need in sludge bioleaching with the aim of residual sludge land application.

Application of lactic acid derived from food waste on pathogen inactivation in fecal sludge: a review on the alternative use of food waste

Food waste generation and disposal have led to several environmental problems, especially in developing countries. This phenomenon is partly because most cities rapidly urbanize, which results in population increase, urban settlement and waste generation. Improper management of waste has continued to create environmental problems. These problems have indeed interfered with the inadequate measures in managing other organic waste such as food waste. Food waste can be fermented and used for pathogen inactivation in fecal sludge (FS). The continual decrease in global crop production due to soil erosion, nutrient runoff and loss of organic matter has generated interest in using FS for soil amendment. However, due to the high number of pathogens in FS that are harmful to humans, FS must be treated before being used in agriculture. Thus, given the high amounts of food waste generated globally and the lactic acid potential of fermented food waste, several researchers have recently proposed the use of fermented food waste to suppress pathogens in FS. This review presents the various approaches in pathogen inactivation in FS using different types of food waste. On the basis of the literature review, the major problems associated with the generation, collection and application of food waste in pathogen inactivation in FS are discussed. Moreover, the trends and challenges that concern the applicability of each method are critically reviewed.