Algae-based biofilm productivity utilizing dairy wastewater: effects of temperature and organic carbon concentration

Design, construction and application of algae-bacteria synergistic system for treating wastewater

The wastewater treatment technology of algae-bacteria synergistic system (ABSS) is a promising technology which has the advantages of low energy consumption, good treatment effect and recyclable high-value products. In this treatment technology, the construction of an ABSS is a very important factor. At the same time, the emergence of some new technologies (such as microbial fuel cells and bio-carriers, etc.) has further enriched constructing the novel ABSS, which could improve the efficiency of wastewater treatment and the biomass harvesting rate. Thus, this review focuses on the construction of a novel ABSS in wastewater treatment in order to provide useful suggestions for the technology of wastewater treatment.

Emerging challenges of the impacts of pharmaceuticals on aquatic ecosystems: A diatom perspective

Pharmaceuticals are a ubiquitous group of emerging pollutants of considerable importance due to their biological potency and potential to elicit effects in wildlife and humans. Pharmaceuticals have been quantified in terrestrial, marine, fresh, and transitional waters, as well as the fauna and macro-flora that inhabit them. Pharmaceuticals can enter water ways through different human and veterinary pathways with traditional wastewater treatment, unable to completely remove pharmaceuticals, discharging often unknown quantities to aquatic ecosystems. However, there is a paucity of available information regarding the effects of pharmaceuticals on species at the base of aquatic food webs, especially on phytoplankton, with research typically focussing on fish and aquatic invertebrates. Diatoms are one of the main classes of phytoplankton and are some of the most abundant and important organisms in aquatic systems. As primary producers, diatoms generate ∼40 % of the world's oxygen and are a vital food source for primary consumers. Diatoms can also be used for bioremediation of polluted water bodies but perhaps are best known as bio-indicators for water quality studies. However, this keystone, non-target group is often ignored during ecotoxicological studies to assess the effects of pollutants of concern. Observed effects of pharmaceuticals on diatoms have the potential to be used as an indicator of pharmaceutical-induced impacts on higher trophic level organisms and wider ecosystem effects. The aim of this review is to present a synthesis of research on pharmaceutical exposure to diatoms, considering ecotoxicity, bioremediation and the role of diatoms as bio-indicators. We highlight significant omissions and knowledge gaps which need addressing to realise the potential role of diatoms in future risk assessment approaches and help evaluate the impacts of pharmaceuticals in the aquatic environment at local and global scales.

Resource recovery using enriched purple phototrophic bacteria in an outdoor flat plate photobioreactor: Suspended vs. attached growth

Purple phototrophic bacteria (PPB) can produce single-cell protein from wastewater at high yields. Growing in a biofilm vs suspended can improve product quality and consistency. This study compares suspended and attached growths of enriched PPB cultures in an outdoor flat plate photobioreactor treating poultry-processing wastewater. Attached growth had lower VFA removal efficiencies (95 ± 2.7 vs 84 ± 6.4 %) due to light limitations and low substrate diffusion rates. Nevertheless, similar overall treatment performances and productivities were achieved (16 ± 2.2 and 18 ± 2.4 gCOD·m^-2·d^-1 for attached and suspended) at loading rates of 1.2-1.5 gCOD·L^-1·d^-1. Biofilms had higher quality than suspended biomass, with lower ash contents (6.9(0.6)% vs 57(16)%) and higher PPB abundances (0.45-0.67 vs 0.30-0.45). The biofilm (20-50 % of the total biomass) might be used as feed and the suspended fraction as fertiliser, improving the economics of the process. Semi-continuous PPB growth outdoors as biofilm is technically feasible, obtaining a superior product without jeopardising performance.

Material biosynthesis, mechanism regulation and resource recycling of biomass and high-value substances from wastewater treatment by photosynthetic bacteria: A review

The environmental-friendly and economic benefits generated from photosynthetic bacteria (PSB) wastewater treatment have attracted significant attention. This process of resource recovery can produce PSB biomass and high-value substances including single cell protein, Coenzyme Q₁₀, polyhydroxyalkanoates (PHA), 5-aminolevulinic acid, carotenoids, bacteriocin, and polyhydroxy chain alkyl esters, etc. for application in various fields, such as agriculture, medical treatment, chemical, animal husbandry and food industry while treating wastewaters. The main contents of this review are summarized as follows: physiological characteristics, mechanism and application of PSB and potential of single cell protein (SCP) production are described; PSB wastewater treatment technology, including procedures and characteristics, typical cases, influencing factors and bioresource recovery by membrane bioreactor are detailed systematically. The future development of PSB-based resource recovery and wastewater treatment are also provided, particularly concerning PSB-membrane reactor (MBR) process, regulation of biosynthesis mechanism of high-value substances and downstream separation and purification technology. This will provide a promising and new alternative for wastewater treatment recycling.

Naturally illuminated photobioreactors for resource recovery from piggery and chicken-processing wastewaters utilising purple phototrophic bacteria

Resource recovery from wastewater, preferably as high value products, has become an integral part of modern wastewater treatment. This work presents the potential to produce single cell protein (SCP) from pre-settled piggery wastewater (PWW) and meat chicken processing wastewater (CWW), utilising anaerobic purple phototrophic bacteria (PPB). PPB were grown as biofilm in outdoors 60 L, 80 L and 100 L flat-plate reactors, operated in sequential batch mode. PPB biofilm was recovered from reactor walls at a total solid (TS) content ∼90 g•L - 1, and the harvested biomass (depending on the wastewater) had a consistent quality, with high protein contents (50-65%) and low ash, potentially applicable as SCP. The COD, N and P removal efficiencies were 71±5.3%, 22±6.6%, 65±5.6% for PWW and 78±1.8%, 67±2.7% and 37±4.0% for CWW, respectively, with biofilm areal productivities up to 14 g TS•m - 2•d - 1. This was achieved at ammonium-N concentrations over 1.0 g•L - 1 and temperatures up to 55 °C and down to 6 °C (daily fluctuations of 20-30 °C). The removal performances and biomass productivities were mostly dependent on the bioavailable COD in the form of volatile fatty acids (VFA). At sufficient VFA availability, the irradiance became limiting, capping biofilm formation. Harvesting of the suspended fraction resulted in increased productivities and recovery efficiencies, but lowered the product quality (e.g., containing undesired inerts). The optimum between quantity and quality of product is dependent on the wastewater characteristics (i.e., organic degradable fraction) and potential pre-treatment. This study shows the potential to utilise sunlight to treat agri-industrial wastewaters while generating protein-rich PPB biomass to be used as a feed, feed additive or feed supplement.

Dairy wastewater management in EU: Produced amounts, existing legislation, applied treatment processes and future challenges

Dairy industry consumes high water amounts and generates highly contaminated wastewater. EU-27 is the second largest milk producer and the main cheese exporter in the world. The main objectives of the current study was to estimate the amounts of dairy wastewater (DWW) that are produced annually in different EU countries and to present the relevant existing EU legislation. The main treatment practices currently applied as well as the future opportunities for sustainable DWW management were also discussed. According to the results a total amount of 192.5 × 10⁶ m³ of DWW are annually produced in EU-27 countries, 49% of them are due to the production of cheeses, while 19%, 18% and 13% are due to the production of drinking milk, acidified milk and butterfat products, respectively. Six countries (Germany, France, Italy, Poland, Spain and Netherlands) contribute to the generation of more than 73% of DWW, while the annual per capita DWW production ranges between 36 L (Luxembourg) and 1441 L (Ireland). Since 2019, EU has established best available techniques (BAT) for the dairy industry in order to achieve efficient monitoring of the produced wastewater, reduced water consumption and increased resource efficiency. The main on-site treatment processes that are currently applied include in series wastewater pretreatment for the removal of fat and pH adjustment, anaerobic or/and aerobic biological processes for the decrease of organic loading and nutrients and use of membranes for the cases that recovered water is going to be reused. Limited information is so far available for the operational treatment cost of the different processes. Data originated from a large dairy industry in Cyprus showed an operational cost equal to 1.21 €/m³ of treated wastewater. The main future challenge for the dairy industry and water treatment sector is the adoption of novel processes aiming to DWW valorization under the frame of circular economy.

Pharmaceuticals and personal care products in aquatic environments and their removal by algae-based systems

The consumption of pharmaceuticals and personal care products (PPCPs) has been widely increasing, yet up to 90-95% of PPCPs consumed by human are excreted unmetabolized. Moreover, the most of PPCPs cannot be fully removed by wastewater treatment plants (WWTPs), which release PPCPs to natural water bodies, affecting aquatic ecosystems and potentially humans. This study sought to review the occurrence of PPCPs in natural water bodies globally, and assess the effects of important factors on the fluxes of pollutants into receiving waterways. The highest ibuprofen concentration (3738 ng/L) in tap water was reported in Nigeria, and the highest naproxen concentration (37,700 ng/L) was reported in groundwater wells in Penn State, USA. Moreover, the PPCPs have affected aquatic organisms such as fish. For instance, up to 24.4 × 10³ ng/g of atenolol was detected in P. lineatus. Amongst different technologies to eliminate PPCPs, algae-based systems are environmentally friendly and effective because of the photosynthetic ability of algae to absorb CO₂ and their flexibility to grow in different wastewater. Up to 99% of triclosan and less than 10% of trimethoprim were removed by Nannochloris sp., green algae. Moreover, variable concentrations of PPCPs might adversely affect the growth and production of algae. The exposure of algae to high concentrations of PPCPs can reduce the content of chlorophyll and protein due to producing reactive oxygen species (ROS), and affecting expression of some genes in chlorophyll (rbcL, psbA, psaB and psbc).

A Review of Microalgal Biofilm Technologies: Definition, Applications, Settings and Analysis

Biofilm-based algal cultivation has many advantages over the conventional suspended growth methods and has received increased attention as a potential platform for algal production, wastewater treatment (nutrient removal), and a potential pathway to supply feedstock for microalgae-based biorefinery attempts. However, the attached cultivation by definition and application is a result of a complex interaction between the biotic and abiotic components involved. Therefore, the entire understanding of the biofilm nature is still a research challenge due to the need for real-time analysis of the system. In this review, the state of the art of biofilm definition, its life cycle, the proposed designs of bioreactors, screening of carrier materials, and non-destructive techniques for the study of biofilm formation and performance are summarized. Perspectives for future research needs are also discussed to provide a primary reference for the further development of microalgal biofilm systems.

Recent advances on food waste pretreatment technology via microalgae for source of polyhydroxyalkanoates

Polyhydroxyalkanoates (PHAs) are biodegradable and biocompatible polyester which are biosynthesized from the intracellular cells of microalgae through the cultivation of organic food waste medium. Before cultivation process, food waste must undergo several pre-treatment techniques such as chemical, biological, physical or mechanical in order to solubilize complex food waste matter into simpler micro- and macronutrients in which allow bio-valorisation of microalgae and food waste compound during the cultivation process. This work reviews four microalgae genera namely Chlamydomonas, Chlorella, Spirulina, and Botryococcus, are selected as suitable species due to rapid growth rate, minimal nutrient requirement, greater adaptability and flexibility prior to lower the overall production cost and maximized the production of PHAs. This study also focuses on the different mode of cultivation for the accumulation of PHAs followed by cell wall destabilization, extraction, and purification. Nonetheless, this review provides future insights into enhancing the productivity of bioplastic derived from microalgae towards low-cost, large-scale, and higher productivity of PHAs.

Application of purple phototrophic bacteria in a biofilm photobioreactor for single cell protein production: Biofilm vs suspended growth

Single cell protein (SCP), has been proposed as alternative to effectively upgrade and recycle organics and nutrients from wastewater. Biomass recovery is a critical issue, and recovery as a biofilm is effective in comparison with sedimentation of suspended biomass. This study aims to determine the applicability of purple phototrophic bacteria (PPB) biofilm on infra-red irradiated, submerged surfaces for the treatment of pre-settled red meat processing wastewater, and SCP generation. PPB removed up to 66% of COD and 42% of TN and TP during batch operation with total areal productivities between 15 and 20 gVS m^-2 d^-1 achieved. More than 60% of the total biomass grew attached (as biofilm) with the remainder being suspended. The biofilm can be harvested at around 160 gTS L^-1 with high protein (>96 g L^-1) and low ash contents (>4.0% compared to >30% in the wastewater). The compositions of attached and suspended biomass differed significantly, where the suspended fraction resembled the wastewater composition (e.g. in terms of inert components). The PPB community was similar in the suspended and biofilm fractions while the biofilm had higher relative abundance of PPB representatives (57% vs 43%). A consistent product composition is highly relevant for the manufacturer and ultimately determines the value as feed, feed additive, or supplement.

Non-suspended microalgae cultivation for wastewater refinery and biomass production

Non-suspended microalgae cultivation technology coupled with wastewater purification has received more scientific attention in recent decades. Since the non-suspended microalgae cultivation is quite different from the suspended ones, the following issues are compared in this study such as advantages and disadvantages, pollutant removal mechanisms and regulations, influential factors, and microalgae biomass accumulation. The analysis aims to support the further application of this technology. The median removal rates of COD, TN, TP, NH₄⁺-N and NO₃^--N were 91.6%, 78.2%, 87.5%, 93.2% and 81.7%, respectively, by non-suspended microalgae under the TN & TP load rates up to 150 mg·L^-1·d^-1. The main pathway for TN & TP removal is microalgae cell absorbance. Light intensity, pollutant composition and microalgae metabolic types are the major factors that influence pollutant removal and the lipid content of microalgae. Meanwhile the mechanism concerning how macro-outer conditions influence the micro-environment and further growth of non-suspended microalgae requires more investigation.

Optimization of the proportions of four wastewaters in a blend for the cultivation of microalgae using a mixture design

A 2nd degree mixture design was used to determine the optimal blend prepared from four wastewater streams to produce microalgae-based biomass. The streams consisted of a liquid digestate from an anaerobic digestion process, a landfill leachate, a septic-system sludge treatment plant liquid, and a wastewater treatment plant effluent. The mixture regression analysis indicated that blends with higher proportions of treated effluent and digestate improved cells growth, while the use of leachate was detrimental to the growth. The global solution of the mixture optimization predicted a maximum value of biomass productivity of 22.76 mg L^-1 d^-1, in a blend consisting of 19% treated effluent, 21% digestate, and 60% water. Proportions of leachate higher than 13.33% were detrimental to the growth. The concentration of ammonia-N in the blends ranged from 0.39 to 150 mg L^-1 d^-1, and its toxicity effect on the cells diminished with increasing amounts of organic carbon in the cultivation medium.

Impact of surface tension of wastewater on biofilm formation of microalgae Chlorella sp

The organic matter and surfactants in wastewater may cause variations in the surface tension of wastewater (STW) ranging between ∼40 and ∼70 mJ·m^-2. This study focused on the influence of STW on microalgae biofilm formation. A theoretical analysis was first conducted, and then microalgae biofilm formation on hydrophilic and hydrophobic substrata in liquid and real wastewater with different surface tensions was studied. The results demonstrated that STW affected microalgae biofilm formation remarkably. When the surface tension of liquid medium (γ^lv) was approximately equal to the average value of surface free energy of microalgae and substrata, biofilm formation reached the minimum. Microalgae biofilm formation on a hydrophilic surface first decreased (from ∼2200 to ∼1500 cells/mm²) and then increased (from ∼1500 to 3100 cells/mm²) with the decrease in γ^lv (from ∼70 to ∼40 mJ·m^-2), whereas biofilm on a hydrophobic surface continued to decrease (from ∼2500 to 1000 cells/mm²).

Nutrient and suspended solids removal from petrochemical wastewater via microalgal biofilm cultivation

Wastewater derived from petroleum refining currently accounts for 33.6 million barrels per day globally. Few wastewater treatment strategies exist to produce value-added products from petroleum refining wastewater. In this study, mixed culture microalgal biofilm-based treatment of petroleum refining wastewater using rotating algae biofilm reactors (RABRs) was compared with suspended-growth open pond lagoon reactors for removal of nutrients and suspended solids. Triplicate reactors were operated for 12 weeks and were continuously fed with petroleum refining wastewater. Effluent wastewater was monitored for nitrogen, phosphorus, total suspended solids (TSS), and chemical oxygen demand (COD). RABR treatment demonstrated a statistically significant increase in removal of nutrients and suspended solids, and increase in biomass productivity, compared to the open pond lagoon treatment. These trends translate to a greater potential for the production of biomass-based fuels, feed, and fertilizer as value-added products. This study is the first demonstration of the cultivation of mixed culture biofilm microalgae on petroleum refining wastewater for the dual purposes of treatment and biomass production.