Mariculture Effluents Research Articles

Efficient treatment of high-salinity aquaculture effluents through synergistic membrane distillation and VUV/UVC photolysis

Effluents from mariculture facilities typically marked contain high salinity and organic loadings, including anti-parasitic chemicals such as formaldehyde. The direct discharge of such effluents poses serious environmental risks, thus requiring the development of sustainable methods for their treatment. Within this context, a novel approach based on the synergistic integration of thermally driven membrane distillation (MD) and vacuum-ultraviolet/ultraviolet-C (VUV/UVC) photolysis is proposed for the treatment of highly polluted saline water without the need of intensive pretreatments or chemical additives. In this specific work, the performances of the proposed integrated treatment process were explored for inland mariculture effluent. The MD system was able to reclaim 90 % of the effluent as distilled water. Concurrently, salts in the MD concentrate were recovered. The subsequent polishing of the MD permeate solution via VUV/UVC photolysis allowed the abatement of the volatiles present in the MD permeate, bringing the concentrations of formaldehyde and total organic carbon (TOC) below the detection limits (0.5 mg L−1 for both techniques) within 20 min of treatment. The novel integrated system improves the purity of the recycled water and serves as an example of sustainable mariculture effluent management, advancing towards zero-liquid discharge within this field.

Optimization of aeration strategies for intensified nitrogen and phosphorus removal in an aerated electrolysis-assisted submerged fixed bed reactor treating recirculating mariculture effluent

Nutrients such as nitrogen (N) and phosphorus (P) discharged from mariculture wastewater pose a serious threat to the environment. In this study, an electrochemically assisted submerged fixed bed bioreactor (E-SFBBR) with intermittent aeration was used to explore the effect of aeration strategies (aeration time, aeration rate and aeration position) on the removal of N and P. Phosphate (PO43--P) removal was maintained above 95% under different aeration strategies. Although PO43--P removal predominantly occurred in the cathode areas, the aeration position affected the main functional area for PO43--P removal by influencing the pattern of DO distribution within E-SFBBR; and chemical precipitation with iron ions was the main removal pathway as revealed by XPS analysis. E-SFBBR with upper aeration (i.e., UA-E-SFBBR), aerated for 6 h d−1 at 0.8 L min−1 showed the best N removal performance, i.e., 83.78 ± 4.67%. The cathode area mainly contributed to N removal through mixotrophic denitrification. Aeration position plays a greater role in affecting N removal compared to aeration time and rate. Upper aeration favored the growth of heterotrophic denitrification bacteria (f_Rhodobacteraceae and Marinicella) in the cathode through providing more anaerobic environment, resulting in a better N removal performance. Besides, results of N transformation pathway predicted by PICRUSt 2.0 revealed that upper aeration promoted the ammonia assimilation but inhibited ammonia oxidation and NO3--N reduction processes in the cathode area. This study provided a theoretical basis for the application of aerated E-SFBBR in mariculture wastewater treatment.

The functional diversity of microbial communities in the multi-compartment biofilters of shrimp mariculture effluents using 16S rRNA metabarcoding

The functional diversity of microbial communities in the multi-compartment biofilters of shrimp mariculture effluents using 16S rRNA metabarcoding

Effects of environment-relevant concentrations of antibiotics on seawater Chlorella sp. biofilm in artificial mariculture effluent

Attached cultivation of microalgae using mariculture effluent could simultaneously realize cost-effective biomass production and effluent polishing, and the obtained microalgal biofilm could be readily applied to aquatic animals that feed directly on biofilms. However, the widespread existence of antibiotics in mariculture effluent may have inhibitory effects on microalgae. Existing studies regarding the influences of antibiotics on microalgae were overwhelmingly mostly conducted in suspended freshwater cultures, and the explored antibiotic concentrations were several orders of magnitudes higher than realist effluent, rendering limited guidance for practical applications. This study, therefore, studied three commonly observed antibiotics in mariculture effluent, i.e. sulfamethoxazole (SMX), tetracycline (TL), and clarithromycin (CLA), and explored their effects on attached seawater Chlorella sp. growth, nutrients removal, and antioxidative properties at environment-relevant concentrations (0.1–200 μg/L). Hormesis was shared among the three antibiotics, and highest biofilm density (14.6 g/m2) was observed under 0.1 μg/L SMX. SMX displayed strongest chlorophyll impairment, while SMX, TL, and CLA respectively favored lipid (up to 42.4 %), protein (up to 39.6 %), and polysaccharides (up to 65.4 %) accumulation. Highest correlation between biofilm density and extracellular polymeric substances (EPS) contents as well as highest total nitrogen (TN) removal were observed under TL exposure, while total phosphorus (TP) removal among all groups met the strictest local discharge standard for mariculture effluent (TP < 0.2 mg/L). Antioxidative responses revealed least stress towards attached seawater Chlorella sp. under TL treatment, while best acclimation under SMX exposure. Potential coping mechanisms of this microalgae under each antibiotic exposure were proposed as well. This study expands the knowledge of microalgae biofilm under environment-relevant concentrations of antibiotics.

Mariculture wastewater treatment using electrochemically assisted submerged fixed bed bioreactor (E-SFBBR): Potential performance and pathways of nitrogen removal

Nitrogen discharged from mariculture industry leads to adjacent aquatic pollution. This study utilized an electrochemically assisted submerged fixed bed bioreactor (E-SFBBR) to treat carbon-limited saline mariculture wastewater and aimed to evaluate the performance and pathways of nitrogen removal by testing the effects of electrical stimulation and different current densities (CD). Electro-stimulation increased nitrogen removal performance of E-SFBBR from 1.1 to 2.2 g N m−2 d−1 to 3.0–3.4 g N m−2 d−1; CD of 0.10 mA cm−2 resulted in the highest N removal rate. Results of water quality at different depths and the batch experiment revealed the N removal pathways in E-SFBBR: in the cathode area, nitrogen removal was mainly attributed to the processes of denitrification and dissimilatory nitrate reduction to ammonia; and in the anode area, nitrification and autotrophic denitrification driven by sulfur or iron contributed to nitrogen elimination. These findings provided a promising method for enhancing N removal from carbon-limited mariculture effluents.

Iron-carbon could enhance nitrogen removal in Sesuvium portulacastrum constructed wetlands for treating mariculture effluents

This study investigated an Iron–carbon (Fe-C) micro-electrolysis method to enhance nitrogen removal of Sesuvium portulacastrum constructed wetlands (CWs) when treating mariculture effluents. The main objective was to investigate the effects of Fe-C on nitrogen purification performance and microbial characteristics of Sesuvium portulacastrum CWs. Results showed that the presence of Fe-C and Sesuvium portulacastrum could improve nitrogen removal efficiency by 20–30% and 15–30%, respectively. CWs with 33% v/v Fe-C addition performed well on nitrogen removal: TAN, 41.49 ± 13.64%; NO2–-N, 13.32%; NO3–-N, 60.02 ± 6.17%; TIN, 63.40 ± 12.11%. Microbial analysis revealed that Fe-C altered the microbial communities, and improved the abundance of denitrification related genera. Based on microbial enzyme activities and genes abundance, the anammox and denitrification processes were promoted by Fe-C in CWs. These findings indicate that Sesuvium portulacastrum CWs with 33% v/v Fe-C represents an effective nitrogen removal for mariculture wastewater with insufficient carbon source.

An integrated, two-step biofiltration system with Ulva fasciata for sequenced removal of ammonia and nitrate in mariculture effluents

Secondary treatment of fishpond effluent is imperative for the removal of excess nitrate and phosphorus. Biofilters comprised of the green macroalgae, Ulva, exhibit several advantages for this process, including usability of the produced edible biomass. However, even low levels of ammonia in fishpond effluent inhibit the uptake of nitrate by Ulva. In order to overcome this drawback we examined Ulva faciata in a two-step biofiltration system. The biofiltration system comprised of two sequenced tanks where the upstream Ulva biofilter was fed directly with mariculture effluent containing both ammonia (as total ammonium nitrogen - TAN) and nitrate (as NO3-N) and the TAN-depleted but NO3-N-rich effluent from this biofilter were transferred to the downstream Ulva biofilter. The performance of each separate Ulva biofilter as well as that of the whole system was measured on a weekly regime over a culture period of three weeks. Between 81 and 95% of the dissolved inorganic nitrogen (TAN + NO3-N) in mariculture effluent was removed by the two-step biofilter, with specific removal of 89–100% of TAN and 57–78% of NO3-N in mariculture effluent by the upstream and downstream Ulva, respectively. Exposure of Ulva in upstream biofilters to higher N input with both TAN and NO3-N did not affect algal production rate, which was relatively similar to that in downstream biofilters fed with TAN-depleted, NO3-N-rich effluent, with mean specific growth rate of 17.85% d−1 (±3.1) in the different biofilters. Removal rates of TAN or NO3-N by upstream and downstream Ulva, respectively, were relatively similar, between 90 and 135 mmol N m−2 d−1, while PO4-P removal was much faster in downstream Ulva biofilters having only NO3-N as a N source. While TAN removal induced production of Ulva biomass with higher N, P and protein content, culture in NO3-N-rich effluent resulted in Ulva biomass with higher lipid content.

A Review on Mariculture Effluent: Characterization and Management Tools

While marine aquaculture, or mariculture, has been growing rapidly and globally in recent decades, many environmental concerns remain to be fully addressed to achieve its long-term goal of sustainable development. This paper aims to provide a synthesized perspective on these issues by reviewing and discussing the characterization, transport, and current modelling and management tools associated with effluents released from mariculture sites. Specifically, we examined the effluent characteristics and behavior from source-to-sink, including the composition and load of effluent discharge, its transport and transformation processes in the water column and at the seabed, and its impacts on the pelagic and benthic environments. We then focused on management-related issues, including the setting of the regulatory mixing zone, the establishment of environmental standards, monitoring measures, and modelling techniques to depict the current state-of-the-art modes in a global context. Our study shows that while substantial progress has been made in understanding the nature of the mariculture effluent, as well as in monitoring and modelling its transport and fate, the regulatory framework still lags behind in many countries where the mariculture industry is relevant. This is particularly evident in the lack of consistent criteria for the definition of regulatory mixing zones and the associated environmental standards for water quality and benthic impacts. Besides, as new predictive models are emerging quickly, their proper evaluation and validation are imperative in view of their increasing application in regulatory practices. This review is intended to provide references for advancing regulatory management of mariculture effluents, as well as for promoting sustainable mariculture development.

Integrated biofilters with Ulva and periphyton to improve nitrogen removal from mariculture effluent

Biofilters composed of Ulva or periphyton reveal great potential in removal of excess nitrogen in mariculture effluent while producing protein-rich edible biomass. However, TAN depletion is requisite to improve nitrate removal performance. In the current study we compared the contribution of Ulva fasciata and periphyton in removal of nitrogen, particularly in the form of nitrate, from fishpond effluent. For this purpose, we integrated U. fasciata or periphyton as a secondary biofilter downstream to a primary U. fasciata biofilter, and measured growth and nutrient removal performance in each of these two-step biofilters and in their constitutuent biofiltration units. The upstream U. fasciata biofilters removed nearly all TAN from fishpond effluent, leaving less than 5 μM of TAN but excess NO3-N in the effluent leaving these biofilters for the downstream biofilters. The downstream U. fasciata biofilter removed 76% of NO3-N from its inlet water. While this was about three times more efficient than its periphyton counterpart, the periphyton's specific removal rate of this nutrient (1.5 g NO3-N g−1 DW d−1) was much faster than that of U. fasciata. Overall, integration of two sequenced U. fasciata biofilters (‘Ulva-Ulva’) yielded more biomass and removed more nitrogen than the Ulva-periphyton biofilter (removing 25 vs. 18 g N wk.−1, respectively). Despite the differences in N removal rate and efficiency, the protein level in upstream U. fasciata and downstream periphyton was relatively similar (~25% DW), while somewhat lower in the downstream U. fasciata. Results of the current study favour the two-step U. fasciata biofilter, but periphyton's faster specific removal of NO3-N and its contribution to oxygen generation should not exclude further improvement of this technology.

Phosphorus and nitrogen removal by a novel phosphate-accumulating organism, Arthrobacter sp. HHEP5 capable of heterotrophic nitrification-aerobic denitrification: Safety assessment, removal characterization, mechanism exploration and wastewater treatment

A novel phosphate-accumulating organism (PAO), Arthrobacter sp. HHEP5 was isolated from mariculture effluents. It produced no hemolysin and was susceptible to most antibiotics. It had removal efficiencies of above 99% for 1–10 mg/L phosphorus at 18–28 °C, pH 5.5–8.5, salinities 0–3%, C/N ratios 5–20, P/N ratios 0.1–0.2 and 20–260 rpm. It exhibited simultaneous aerobic phosphorus removal, nitrification and denitrification with the highest ammonium, nitrite, nitrate removal efficiencies of 99.87%, 100%, 99.37%. Phosphorus removal was accomplished by assimilating phosphate with the existence of polyphosphate kinase completely under aerobic condition. Genes involved in nitrogen removal were amplified. 99% of phosphorus and 95% of nitrogen in both mariculture and domestic wastewater were removed by HHEP5. This study provided sound methods for future screening of PAOs and new perspectives for renewed cognition of phosphorus removal process. Wide adaptation and remarkably aerobic phosphorus, nitrogen removal performances would make HHEP5 a promising candidate in wastewater treatment.

Microbial community and interspecies interaction during grazing of ark shell bivalve (Scapharca subcrenata) in a full-scale bioremediation system of mariculture effluents

A novel biological approach using ark shell bivalves as potential species for remediation of effluents was studied to determine the microbial community interspecies interaction and nutrient cycling in a restoration system of mariculture effluents. A field study showed that Scapharca subcrenata was the main driver of the microbial community's interspecies-interaction (PERMANOVA, R = 0.0572, P = 0.005) in the treatment zone (TZ). Analysis of co-occurrence networks based on random matrix theory (RMT) indicated that the network's complexity parameters were enhanced in the TZ and disrupted in the control zone (CZ) due to eutrophic disturbances. Concurrently, the TZ was correlated with more profound network modifications (i.e., higher modularity, total nodes (n), cohesion, and proportion of positive links), suggesting that S. subcrenata influenced microbial interspecies interactions in the system. Similarly, the co-occurring networks of generalists Proteobacteria (OTU2037) at genus Anaerospora and Actinobacteria (OTU9660) at genus Candidatus aquiluna for anaerobic ammonia-oxidation (ANAMMOX) were highly significant in the TZ. The top-down and bottom-up forces of S. subcrenata influenced the removal efficiency of nitrogenous compounds by reducing 81.51% of nitrite (NO2−-N), 84.61% of total ammonium nitrogen (TAN) and 72.78% of nitrate (NO3−-N). Generally, the introduction of ark shell bivalve (S. subcrenata) to the system as a biofilter provides a very low-cost bioremediation technology that could be one of the best restorations and remediation tools for mariculture effluents.

Culturable heterotrophic nitrification-aerobic denitrification bacterial consortia with cooperative interactions for removing ammonia and nitrite nitrogen in mariculture effluents

Nitrogen pollution from ammonia and nitrite has been a significant environmental concern in the aquaculture industry. Current studies mostly focus on the characteristics of heterotrophic nitrification and aerobic denitrification (HNAD) bacteria isolated from freshwater environments such as domestic wastewaters, whereas HNAD bacteria in mariculture have yet to be well understood. Herein, this study aimed to investigate the interactions between culturable HNAD bacteria from mariculture environments by combining high-throughput sequencing and traditional cell culture method, in order to develop potential microbial consortia for high-efficiency nitrogen removal in mariculture effluents. By twenty-five species of halophilic HNAD bacteria co-cultured in the synthetic mariculture effluent (ammonia: 20 mg/L, C/N: 5), ammonium removal was mainly driven by the cooperative interactions between strains from Marinomonas, Marinobacterium, Halomonas, and Cobetia. Due to the interspecific coexistence, three novel bacterial consortia of Marinomonas communis &Halomonas titanicae, Marinomonas aquimarina &Halomonas titanicae, and Marinomonas aquimarina &Cobetia marina exhibited significantly better ammonium removal efficiency and stability than single strains. Meanwhile, Marinomonas communis &Halomonas titanicae showed the highest nitrite removal rate of 0.76 mg NO2−-N/L/h. Importantly, these microbial consortia could convert more inorganic-N into bacterial biomass by assimilation and dissimilation instead of the increased nitrogen lost by denitrification. These findings will contribute to understanding and developing the culturable HNAD bacterial consortia for controlling inorganic-N pollution in mariculture effluents or other saline wastewaters.

Carbon sources derived from maize cobs enhanced nitrogen removal in saline constructed wetland microcosms treating mariculture effluents under greenhouse condition.

This study investigated an alternative carbon source derived from maize cobs (MCs) to enhance nitrogen removal in saline constructed wetlands (SCWs). The main objectives were to select the proper pretreatment method of MCs for rapid carbon release; and to investigate the effects of maize cob pieces (i.e. MCP) and three addition levels of maize cob lixiviums (i.e. L-MCL, M-MCL and H-MCL) on nitrogen purification performance and microbial characteristics of SCWs. Results showed NaOH pretreatment enhanced carbon release of MCs in seawater (from 7.5±0.4 mgCOD g-1 to 16.4±0.2 mgCOD g-1). The 80-d trial showed SCWs with M-MCL addition performed well on nitrogen removal: NO3-N, 88.8±11.6%; NO2-N, 91.1±3.5%; TAN, 96.5±1.6%; TIN, 89.8±10.4%; with 2mgL-1 effluent COD. Denitrification parameters confirmed MCL to be a high quality carbon source: denitrification potential (PDN)=0.16 gN gCOD-1; heterotrophy anoxic yield coefficient (YH)=0.54 gCOD gCOD-1. The MCP and H-MCL treatments improved substrate dehydrogenase activity, indicating a higher microbial activity in these SCWs. Sequencing analysis revealed that, regardless of addition manners, carbon sources from MCs changed the rhizosphere microbial community. At genus level, Anaerophaga (10.1%), Granulosicoccus (8.2%) and Sulfurimonas (6.6%) dominated in SCWs under MCP treatment. Increased MCL addition levels improved the relative abundance of Vibrio, Malonomonas and Caldithrix, suggesting the enhancement of denitrification. Relative high proportions of Desulfotignum and Desulfovibrio, and Sulfurimonas were observed in MCP and H-MCL SCWs, implying that sulfate reduction occurred in SCWs with excess carbon sources.

An integrated Ulva-periphyton biofilter for mariculture effluents: Multiple nitrogen removal kinetics

Biofilters made of Ulva and periphyton differ in their effectiveness in removing ammonia and nitrate from mariculture effluents. Our research evaluated the practicality of a combination of these two biofilters in improving the overall removal of dissolved N, where efficient removal of ammonia by the seaweed is followed by efficient removal of nitrate by periphyton. A paired Ulva-periphyton biofilter was exposed to various areal loads of ammonia and nitrate, the primary nitrogen forms in fishpond effluents.A first upstream macroalgae biofilter stocked with Ulva was fed with fishpond effluents at different areal loads of ammonia and nitrate, while a second downstream periphyton biofilter was paired for further nitrogen removal from the effluent. Ulva removed ammonia at a rate of 0.7–5.4 g TAN m−2 d−1, in correlation with the TAN areal load, with Vmax of 5.1 and Km of 4.4 g TAN m−2 d−1. Downstream periphyton was exposed to a lower TAN, but nitrate-rich effluent, and revealed similar capacities for the removal of both N forms, at removal rates of up to 1.7 and 1.8 g N m−2 d−1, respectively. Compared to nitrate, areal load of TAN had a greater impact on the removal dynamics of both N forms by periphyton. Overall, the paired biofilter resulted in a nearly total depletion of ammonia (97%) and efficient nitrate removal (67%), when areal loads in fishpond effluents were below 2 and 4 g N m−2 d−1 of TAN and NO3-N, respectively.

Is Ulva sp. able to be an efficient biofilter for mariculture effluents?

Nitrogenous compounds such as ammonia, nitrate, and dissolved organic nitrogen (DON) are the main waste components of marine fish pond effluents. These compounds are also regarded as the primary nitrogen sources for seaweed. Aiming at designing an efficient and cost-effective extractive biofilter for fishpond effluents, Ulva lactuca performance and the dynamics of dissolved inorganic (DIN) and DON uptake by this alga grown in the effluents of a land-based integrated multi-trophic aquaculture (IMTA) system were studied. Stocking densities of 1 and 3 kg m−2 were found to be optimal for yield along with specific growth rate (SGR) and protein content, respectively. The presence of ammonia inhibited nitrate uptake by U. lactuca and carbon limitation reduced SGR and yield. However, protein levels of U. lactuca tissue in a carbon-limited situation were higher than when unlimited carbon was made available. When compared with 3 kg m−2 stocking densities, the high C/N ratio in U. lactuca tissue cultured at 1 kg m−2 likely indicated carbon limitation. Ammonia assimilation rate was density dependent. At 1 kg m−2, ammonia uptake was relatively fast, at 4.31 μmole N h−1, and nitrate uptake started only 24 h after ammonia depletion, suggesting this period to be the time required for nitrate reductase (NR) synthesis in the algae tissue. At 2 kg m−2, ammonia uptake was 2.51 μmole N h−1 and nitrate uptake started 24 h after that observed in 1 kg m−2, suggesting that the lower ammonia threshold for uptake by the U. lactuca is around 1.4 μmole L−1. Contrary to 1 and 2 kg m−2 stocking densities, in the 3 kg m−2 stocking density, ammonia uptake was as low as 1.51 μmole N h−1 and no uptake of nitrate appeared to have taken place due to the presence of ammonia in the water. The additional ammonia in the water was found to be due to DON-ammonifying bacteria on the surface of U. lactuca thalli. In the 1ow stocking density, the additional ammonia was relatively low compared to that measured at the high algae density. In the light of the better understanding of the system dynamics achieved in our study, we hypothesize that a set of similar bioreactors using U. lactuca can intensify the system purification efficiency manifold.

Combinations of Ulva and periphyton as biofilters for both ammonia and nitrate in mariculture fishpond effluents

Periphyton-based biofilters for aquaculture effluent possess multiple advantages, in water oxygenation, CO2 reduction and production of useful biomass. The performance of a marine periphyton biofilter, in terms of uptake rate and efficiency in removing different forms of nitrogen, was investigated. A periphyton biofilter was paired with an upstream macroalgae biofilter stocked with Ulva to expose the periphyton to ammonia-depleted but nitrate-rich effluent. Three trials compared the removal of total ammonia-N (TAN), nitrate (NO3-N), total N and phosphorus. The biofiltration and growth performance of (1) the periphyton downstream to the Ulva tank, (2) periphyton alone and (3) Ulva alone were compared. Biofiltration performance was evaluated at different areal loads of TAN and NO3-N.Periphyton growth performance did not depend on the effluent nutrient composition or on N loads, and yielded between 7.3 and 10.6 g dry weight m−2 d−1. While the Ulva preferred uptake of TAN over NO3-N, the periphyton showed no preference between them, demonstrating flexible shifts between TAN and NO3-N uptake. TAN uptake rate by the periphyton was not influenced by the effluent composition. However, periphyton NO3-N uptake rate and efficiency rose about fivefold, up to 1.4 g NO3-N m−2 d−1 and 63%, respectively, upon depletion of TAN areal load below 0.18 g N m−2 d−1 (<0.3 mg L−1) by the Ulva pre-treatment. Normalizing nutrient uptake rate to biomass revealed similar uptake rate of TAN and phosphorus by periphyton and Ulva, while the periphyton took up nitrate much faster.By removing up to 76% of the total nitrogen, with specific removal efficiency of 97% of the TAN and of 67% of the NO3-N, the novel dual Ulva-periphyton biofilter revealed a synergistic potential in treatment of nutrient-rich mariculture effluents.

Water quality, ecological processes and management procedures in a periphyton biofiltration system in mariculture: A statistical analysis

A periphyton biofiltration system of mariculture effluents was studied to identify ecological processes and management procedures that strongly affect the biofilter functioning, in order to attain optimal biomass production and nutrient removal. The multivariate statistical technique of factor analysis allowed reducing the large amount of data available into three main factors. The first factor, which accounted for 49% of the overall data variability, was herein called “biological activity” as it represents the joint effects on the variables measured of photosynthesis, N and P uptake, respiration and decomposition of organic matter. The second and third factors were “autotrophic biomass density” and “nitrite and phosphate uptake/release balance”, which, respectively, accounted for further 20% and 14% of the data variability. A conceptual model, describing the functioning of the periphyton biofilters, revealed a delicate equilibrium among the different processes, whose understanding help to manage the biofilters towards optimal production of periphytic biomass and nutrient removal. Raising flow rate raised the overall nutrient uptake rate but reduced uptake efficiency and diluted nitrifying particles. A reduced flow rate led to sedimentation of organic particles, decomposition and nutrients re-mineralization. Apparently, control of water flow and nutrient content, periphyton substrate area and the cleaning of the effluent supply system are key management elements for the operation of a periphyton-based biofilter system that maximizes both periphyton biomass production and nutrient removal.

Towards a marine biorefinery through the hydrothermal liquefaction of macroalgae native to the United Kingdom

Hydrothermal liquefaction (HTL) is a promising biomass conversion method that can be incorporated into a biorefinery paradigm for simultaneous production of fuels, aqueous fertilisers and potential remediation of municipal or mariculture effluents. HTL of aquatic crops, such as marine macro- or microalgae, has significant potential for the UK owing to its extensive coastline. As such, macroalgae present a particularly promising feedstock for future UK biofuel production. This study aimed to bridge the gaps between previous accounts of macroalgal HTL by carrying out a more comprehensive screen of a number of species from all three major macroalgae classes, and examining the correlations between biomass biochemical composition and HTL reactivity. HTL was used to process thirteen South West UK macroalgae species from all three major classes (Chlorophyceae, Heterokontophyceae and Rhodophyceae) to produce bio-crude oil, a bio-char, gas and aqueous phase products. Chlorophyceae of the genus Ulva generated the highest bio-crude yields (up to 29.9% for U. lactuca). Aqueous phase phosphate concentrations of up to 236 mg L−1 were observed, obtained from the Rhodophyta, S. chordalis. Across the 13 samples, a correlation between increasing biomass lipids and increasing bio-crude yield was observed, as well as an increase in biomass nitrogen generally contributing to bio-crude nitrogen content. A broader range of macroalgae species has been examined than in any study previously and, by processing using identical conditions across all feedstocks, has enabled a more cohesive assessment of the effects of biochemical composition.

Marine periphyton biofilters in mariculture effluents: Nutrient uptake and biomass development

Cost of effluent treatment, water quality maintenance and feeds constitute most of aquaculture's operational costs, and influence its sustainability. The present study examined the effectiveness of periphyton for biofiltration of mariculture effluents. Marine periphyton was allowed to spontaneously develop on a plastic net substrate, in experimental bioreactors that were fed with effluents from fish mariculture ponds. Biomass development and nutrient uptake were followed over four seasons. Attention was given to the orientation and area of the net substrate, season and additional operational factors. The highest specific growth rate (SGR) of 27% day−1 was measured during the second week of periphyton growth in the summer. Mean daily periphyton production rates in the spring and autumn were 2.4 and 1.8g (ash-free dry weight) m−2day−1, respectively. The vertical orientation of the net substrate was overall advantageous over the horizontal orientation. Increasing the substrate area of vertically oriented nets in the biofilter increased the removal efficiency of total ammonia nitrogen (TAN) up to 80%, and allowed more biomass production in the biofilter. Multiple polynomial regression models suggest strong effect of biomass weight and effluent retention time on the removal efficiency of TAN and dissolved inorganic nitrogen (DIN). The removal rates of TAN and DIN in these experiments were between 0.11 and 1.2gNm−2 (substrate area) day−1 for periphyton at the age of 7 and 42days, respectively. Marine periphyton seems to be a simple, low cost and sustainable component, which can perform biofiltration/rehabilitation of water quality and potentially serve as feed for fish and shrimp.

Management of Ulva lactuca as a biofilter of mariculture effluents in IMTA system

article i nfo Seaweed IMTA biofilter Ulva lactuca Aeration Economics A strong aeration evens out light exposure, facilitates solute diffusion and increases yield in macroalgae cultivation. It is also responsible however, for up to 85% of the operating cost in the treatment of fish pond effluents. Optimizing and reducing excess aeration can therefore diminish the overall operation cost in monoculture and in Integrated Multi Trophic Aquaculture (IMTA). Biofiltration efficiency and crude biochemical composition of Ulva lactuca ponds were compared at two aeration regimes (continuous and 15 s min -1 intermittent aeration) in