Bioethanol production from Chlorella vulgaris ESP-31 grown in unsterilized swine wastewater

Poultry litter extract as solid waste supplement for enhanced microalgal biomass production and wastewater treatment

Wastewater and livestock waste can be used as a cheap source of nutrients for microalgae growth. In this work, a cocktail waste medium (CWM) was developed using 75% Chhalera municipal wastewater (C-MWW), 25% Parag dairy wastewater (P-DWW), and 15 g L-1 of poultry litter extract (PLE-15) for low-cost cultivation of Chlorella sp. BRE4. The highest specific growth rate of 0.57 day-1 and biomass productivity of 315 mg L-1 day-1 was found in CWM. Microalgae grown in the photobioreactor with the strategic supply of PLE (PBR-4) resulted in the highest lipid productivity of 113.5 mg L-1 day-1, which was 1.3 and 5.4 times of PBR-3 (PLE supplemented since day 1) and PBR-1 (no additional PLE), respectively. The carbohydrate content (30.45%) in PBR-4 showed a 1.33-fold increase than PBR-1, confirming the suitability of the strategy for enhancing carbohydrates and lipids simultaneously. The high removal percentage of total nitrogen (92.6%) and phosphorus (97.4%) from CWM under strategic supply conditions demonstrated Chlorella sp. BRE4 is a suitable candidate for waste valorization and biofuel production.

Principles, challenges, and optimization of indigenous microalgae-bacteria consortium for sustainable swine wastewater treatment

Indigenous microalgae-bacteria consortium (IMBC) offers significant advantages for swine wastewater (SW) treatment including enhanced adaptability and resource recovery. In this review, the approaches for enriching IMBC both in situ and ex situ were comprehensively described, followed by symbiotic mechanisms for IMBC which involve metabolic cross-feeding and signal transmission. Strategies for enhancing treatment efficiencies of SW-originated IMBC were then introduced, including improving SW quality, optimizing system operating conditions, and adjusting microbial activities. Recommendations for maximizing treatment efficiencies were particularly proposed using a decision tree approach. Moreover, removal/recovery mechanisms for typical pollutants in SW using IMBC were critically discussed. Ultimately, a technical route termed SW-IMBC-Crop-Pig was proposed, to achieve a closed-loop economy for pig farms by integrating SW treatment with crop cultivation. This review provides a deeper understanding of the mechanism and strategies for IMBC's resource recovery from SW.

Effects of microalgal (Tetradesmus obliquus MCX38) attachment on photobioreactor treatment efficiency of raw swine wastewater

Attachment of microalgae on the inner surfaces of photobioreactors impacts the efficiency of swine wastewater treatment by reducing the light intensity, which has been overlooked in previous studies. This study investigated the relationship between microalgal attachment biomass and light intensity in photobioreactors, determined the optimal attachment time for effective pollutant removal, and clarified the mechanisms of microalgal attachment in swine wastewater. After 9 days of treatment, the attached biomass in the photobioreactor increased from 0 to 6.4 g/m2, decreasing the light intensity from 2,000 to 936 lux. At the 24 h optimal attachment time, the concentrations of chemical oxygen demand, ammonia nitrogen, and total phosphorus decreased from 2725.1, 396.4, and 87.2 mg/L to 361.2, 4.9, and 0.8 mg/L, respectively. Polysaccharides in the extracellular polymeric substances released by microalgae play a significant role in facilitating microalgae attachment. Optimizing the microalgal attachment time within photobioreactors effectively mitigates pollutant concentrations in swine wastewater.

Recent advances in swine wastewater treatment technologies for resource recovery: A comprehensive review

Swine wastewater (SW), characterized by highly complex organic and nutrient substances, poses serious impacts on aquatic environment and public health. Furthermore, SW harbors valuable resources that possess substantial economic potential. As such, SW treatment technologies place increased emphasis on resource recycling, while progressively advancing towards energy saving, sustainability, and circular economy principles. This review comprehensively encapsulates the state-of-the-art knowledge for treating SW, including conventional (i.e., constructed wetlands, air stripping and aerobic system) and resource-utilization-based (i.e., anaerobic digestion, membrane separation, anaerobic ammonium oxidation, microbial fuel cells, and microalgal-based system) technologies. Furthermore, this research also elaborates the key factors influencing the SW treatment performance, such as pH, temperature, dissolved oxygen, hydraulic retention time and organic loading rate. The potentials for reutilizing energy, biomass and digestate produced during the SW treatment processes are also summarized. Moreover, the obstacles associated with full-scale implementation, long-term treatment, energy-efficient design, and nutrient recovery of various resource-utilization-based SW treatment technologies are emphasized. In addition, future research prospective, such as prioritization of process optimization, in-depth exploration of microbial mechanisms, enhancement of energy conversion efficiency, and integration of diverse technologies, are highlighted to expand engineering applications and establish a sustainable SW treatment system.

Strategies for livestock wastewater treatment and optimised nutrient recovery using microalgal-based technologies

Global sustainable development faces several challenges in addressing the needs of a growing population. Regarding food industries, the heightening pressure to meet these needs has resulted in increased waste generation. Thus, recognising these wastes as valuable resources is crucial to integrating sustainable models into current production systems. For instance, the current 24 billion tons of nutrient-rich livestock wastewater (LW) generated yearly could be recovered and valorised via biological uptake through microalgal biomass. Microalgae-based livestock wastewater treatment (MbLWT) has emerged as an effective technology for nutrient recovery, specifically targeting carbon, nitrogen, and phosphorus. However, the viability and efficacy of these systems rely on the characteristics of LW, including organic matter and ammonium concentration, content of suspended solids, and microbial load. Thus, this systematic literature review aims to provide guidance towards implementing an integral MbLWT system for nutrient control and recovery, discussing several pre-treatments used in literature to overcome the challenges regarding LW as a suitable media for microalgae cultivation.

A microscale system for in situ investigation of immobilized microalgal cell resistance against liquid flow in the early inoculation stage

In attached microalgae cultivation systems, cell detachment due to fluid hydrodynamic flow is not a subject matter that is commonly looked into. However, this phenomenon is of great relevance to optimizing the operating parameters of algae cultivation and feasible reactor design. Hence, this current work miniaturizes traditional benchtop assays into a microfluidic platform to study the cell detachment of green microalgae, Chlorella vulgaris, from porous substrates during its early cultivation stage under precisely controlled conditions. As revealed by time lapse microscopy, an increase in bulk flow velocity facilitated nutrient transport but also triggered cell detachment events. At a flow rate of 1000 μL min-1 of growth medium for 120 min, the algal cell coverage was up to 5% lower than those at 5 μL min-1 and 50 μL min-1. In static seeding, the evolution of attached cell resistance toward liquid flows was dependent on hydrodynamic zones. The center zone of the microchannel was shown to be a "comfortable zone" of the attached cells to sequester nutrients effectively at lower medium flow rates but there was a profile transition where outlet zones favored cell attachment the most at higher flow rates (1.13 times higher than the center zone for 1000 μL min-1). Besides, computational fluid dynamics (CFD) simulations illustrated that the focusing band varied between cross-sections and depths, while the streamline was the least concentrated along the side walls and bottom plane of the microfluidic devices. It was intriguing to learn that cell detachment was not primarily happening along the symmetry streamline. Insight gained from this study could be further applied in the optimization of operating conditions of attached cultivation systems whilst preserving laminar flow conditions.

Treatment and utilization of swine wastewater - A review on technologies in full-scale application

The management of swine wastewater has become the focus of attention in the farming industry. The disposal mode of swine wastewater can be classified as field application of treated waste and treatment to meet discharge standards. The status of investigation and application of unit technology in treatment and utilization such as solid-liquid separation, aerobic treatment, anaerobic treatment, digestate utilization, natural treatment, anaerobic-aerobic combined treatment, advanced treatment, are reviewed from the full-scale application perspective. The technologies of anaerobic digestion-land application is most appropriate for small and medium-sized pig farms or large pig farms with enough land around for digestate application. The process of "solid-liquid separation-anaerobic-aerobic-advanced treatment" to meet the discharge standard is most suitable for large and extra-large pig farms without enough land. Poor operation of anaerobic digestion unit in winter, hard to completely utilize liquid digestate and high treatment cost of digested effluent for meeting discharge standard are established as the main difficulties.

Bioremediation of zinc and manganese in swine wastewater by living microalgae: Performance, mechanism, and algal biomass utilization

The remediation effects of living Chlorella sp. HL on zinc and manganese in swine wastewater was investigated, and the responses of algal cells and the mechanism were explored. In the wastewater with Zn(II) concentration of 1.85 mg/L and Mn(II) of 1 or 6 mg/L, the highest removal of Zn(II) by Chlorella reached 86.72% and 97.16%, respectively, and the Mn(II) removal were 42.74% and 30.33%, respectively. The antioxidant system of cells was activated by a significant increase in superoxide dismutase and catalase enzyme activities and a significant decrease in malondialdehyde in the mixed system compared to the single system. The presence of Mn(II) could positively regulate the differentially expressed genes related to catalytic activity and metabolic processes between the single Zn system and the mixed systems, reducing the stress of Zn(II) on Chlorella and more favorable to chlorophyll synthesis. The heavy metal-containing microalgal biomass obtained has the potential as feed additives.

Growth-promoting effects of phytohormones on capillary-driven attached Chlorella sp. biofilm

Using low strength wastewater for microalgae cultivation is challenged by slow growth and biomass harvesting issue in suspended systems, and growth-promoting effects of phytohormones at currently recommended dosages could neither obtain high enough biomass concentrations nor economic feasibility. This study aims to solve the issues of slow growth, biomass harvest, and phytohormone costs altogether by supplementing low dosage phytohormones in an improved capillary-driven attached cultivation device. The device displayed nutrients-condensing properties, and dosages of indole acetic acid (IAA), 6-benzylaminopurine (6-BA), and salicylic acid (SA) for highest microalgal growth were respectively 10-6 M, 10-6 M, and 10-7 M, being at least one order of magnitude lower than in suspended cultures. SA was most effective in growth-promoting (up to 7.0 g/m2 biomass density) and nutrients uptake (up to 98.6 % from the bulk environment), while IAA was most effective in antioxidative defenses. These results provided new insights in cost-effective and harvesting-convenient microalgae production.

Performance and mechanism of Chlorella in swine wastewater treatment: Roles of nitrogen-phosphorus ratio adjustment and indigenous bacteria

The effects of adjusting the nitrogen-phosphorus (N/P) ratio of wastewater and indigenous bacteria on swine wastewater treatment by Chlorella sp. HL were investigated. The optimal N/P ratio of Chlorella in swine wastewater was 20 by adjusting the phosphorus concentration. The participation of indigenous bacteria increased total extracellular polymeric substances content, which was beneficial to maintain the stability of the algal-bacterial consortium, and improved the algal density and the removal rate of total nitrogen, total phosphorus, and chemical oxygen demand by 47.8%, 24.0%, 30.7%, and 326.7%, respectively. Proteobacteria was the dominant phylum with the relative abundance of 71.58% in the algal-bacterial system at optimal N/P ratio, and Brevundimonas, Chryseobacterium, and Pseudomonas played positive roles in the establishment of symbiotic systems at the genus level. These results provide a theoretical basis for the construction of an efficient algal-bacterial symbiotic system in swine wastewater treatment and support for commercial scale-up.